Isolated Thunderstorms East/Sct'd West - Some Strong Late

Active Shortwave trough has developed on the SW Corner of Cut off,quasi-stationary upper level cold core low over Western Illinois. The low itself has retrograded to a small degree in 48 hours toward the SW from Lake Michigan. Strong/severe storms possible along that S/W trough. Pressure gradient aloft over Florida is relaxing due to the now even greater distance from Florida, although minute, effective. TUTT low north of the Dominican Republic and High Pressure over the Atlantic producing sinking motion over a layer of shallow , moist air over the Atlantic east of the Gulf Stream. Disturbance, likely enhanced by the Gulf Stream east of Florida is advecting toward North Carolina Coast today

THE BIG PICTURE, SYNOPSIS: The upper level, cold core low over Lake Michigan yesterday (which resulted in a number of waterspouts due to the warmer lake waters and very cold air aloft) has retrograded into West Central Illinois. This depiction was indicated by some of the models yesterday to occur. Meanwhile, a frontal boundary has evolved arcross Arkansas into Southern Illinois, which will gradually wrap into the parent low pressure system tonight and become a part of the occluded boundary further north.


Further South, as a result of the upper low retrograding, the pressure gradient aloft has weakened as if it wasn't weak enough already the past two days, although the overall 'troughing' is digging deeper into the Northern Gulf to the west of the state. Showers have erupted as result over the Gulf and are moving across Coastal SW and West Central Florida at noon time, with additional showers along the east coast. Otherwise, moisture amounts remain high at 2.00+" universally, which is well above the norm for this time of year, as sensed by the muggy conditions outside. Instability is highest just off shore the Cape to JAX with most areas fairly uniform in that department. 


There seems to be a bit of mid-level drying late this morning along the east half of the state north of Lake Okeechobee, possibly due to some subsidence on the backside of the offshore trough.


 As a result, cumulus cloud lines forming along the intracoastal are not gaining as much height as they would otherwise. SW Steering toward the NE seems much stronger in satellite animations on the west side of the state, but dwindles to  nearly neutral in the interior and east side.  Otherwise, conditions would be favorable for waterspouts along the east coast through 2pm, but so far that possibility seems all but naught due to slightly drier layer aloft, as observed by the downdraft CAPE portrayed on  the SPC mesoanalysis page selection for that parameter.

Latest Mesoscale Analysis from the SPC website shows Downdraft CAPE on the east side of the state. This parameter is a good indicator for strong winds in thunderstorms in downdrafts, but is also an indicator depending on other parameters that storms might have a hard time getting started without a trigger, of which in the case of today there does not appear to be one other than lake and sea breeze mergers. 

TODAY: Activity should have no problem initiating as already observed from SE Florida and up the west coast. However, the further North and East one goes, so does the steering currents weaken to almost zero in the area of downdraft Cape. That factor, combined with the presence of some drier air aloft should inhibit thunderstorm (showers still possible though along the sea breeze) development through early-mid afternoon along the east coast except perhaps toward Lake Okeechobee/Martin/St. Lucie/Interior Palm Beach Counties. Showers are already becoming scattered South, but thunder remains isolated,  and with temperatures aloft no different than yesterday expect that persistence should rule the roost today. 


Thus, like the past two days, despite forecasts of model guidance and numerical guidance for scattered thunderstorms, that has yet to be the case. Thus, persistence seems the most appropriate approach until proven otherwise. 


It should be noted that the Mesoscale analysis page for parameters aloft is only as good as atmospheric soundings taken every 12 hours across the state at TPA/MIA/XMR  (KSC)/TLH/JAX/and EVW (Key West). Otherwise, the parameters portrayed are based largely on, you guessed it, a Model (the RUC). Thus, any inconsistencies with the RUC model are reflected in graphics such as that above. I have seen values vary considerably over a 3 hour window of time, but as of early this morning the downdraft CAPE has done nothing but increase..so that seems to be the trend for the first 1/2 of the day at least. Note how all the showers on this radar over lay (above) are occurring where there is no down draft CAPE.


THIS AFTERNOON: Sea breezes will set up along both coasts. The east coast sea breeze combined with a lake breeze (Lake Okeechobee) could trigger a strong storm or series of propagating storms either to the north or south toward the East Side of the Lake with lightning and wind gusts being the main danger factors, although a funnel cloud or even landspout could occur with any of that activity as well.


Elsewhere, showers/Storms will form over the SW/W side of the state along the incoming west coast sea breeze. Showers and a few thunderstorms could form anywhere over South Florida and move very little. Again, propagation along the sea breeze and lake breeze boundaries, as well as shower/storm outflow boundaries, will dictate the erratic storm motions in South Florida.


Further north, any activity along Lake Okeechobee could send outflow northward in the very light steering which nearly parallels the coast today, which too can work north with time along the east coast sea breeze. 


However, by that time the sea breeze could be well west of I95 north of Vero Beach or Ft. Pierce. There is one big question though concerning this one tiny but important factor. 


That being, SW to NE steering might increase later today as the shortwave over Arkansas digs deeper toward Northern Louisiana. Granted , that is a long way away, but there is a domino affect which could translate east and south with time. As of now, it appears that will be the case on Monday with all things else remaining the same with the upper low still in place in generally the same location...including moisture over Florida...storms might be more active along the East Coast sea breeze. It is worth noting though with cut off lows, the models as has been cited time and time again, inevitably try to move them out too quickly. 


Thus, Monday/Tuesday's forecast despite what morning guidance reads (which has not all come out yet), could easily be incorrect when it comes down to the finer, more critical factors in the rain bucket department. Thus, I didn't bother waiting for it to become available, it has proven worthless.

 
Best Guess at this point today. Realizing for most of these early in the day forecasts one has to second guess the model guidance and remain one step ahead of what they actually show, one must project and a bit of a 'means of experience'.  Afterall, ccording to the RUC,   showers  would already be in progress around the Space Center. Not going to happen any time soon...with nearly clear skies at noon.


Showers/storms/and outflows should spread west and north with time, eventually meeting up with the east coast sea breeze west of I-95 (if not further west) after 3pm, and perhaps much later.


The other problem at this time of year is that during peak heating some of the low level moisture mixes out in the absence of any convective inhibition which is the case right now. Thus, the storms do not really 'jack up' until the sun gets low in the sky and dewpoint depressions can lower, or rather, the ambient outside air temperature can lower to meet the dew points. Thus, the most strong activity outside of near Lake Okeechobee and maybe a storm or two over South Florida will be delayed until after 4-5pm...perhaps later. 


Outflows both from the west coast and up the east coast (toward extreme SW Brevard and Osceola County) will possibly foster more outflows to drive the east coast sea breeze further yet inland.


Peak of the strongest activity should be toward Northern Interior as was the case the past 3 days (there's that word 'persistence' again), in or near locations since as the Ocala National Forest where dew-point depressions recover the quickest due to all the vegetation there), and toward Gainesville. Upper level steering should be a bit stronger further north as well, so although not expecting a big coverage of thunder, it could be strong.


The least  chance of seeing rain today will be far East Central, however, with the steering potentially increasing very late today into tonight  combined with remaining boundaries around ..with the factor that the east coast sea breeze will be easing off and and dissolving , some showers/inland storm debris light rains/or even a thunderstorm could impact the near coastal areas near Rockledge/Titusville/Palm Bay and north toward DAB near or after dark through 10-11pm. Very isolated.


TUESDAY: This now seems to be the better day for the East Coast anywhere to receive rain. But then again, that was what the case was previously thought to be for yesterday and today.


BEYOND: High pressure is thought to build eastward behind the shortwave trough toward Florida, putting much of the state in sinking, more northerly component steering ahead of it, and also squeezing out atmospheric moisture, thus lower rain chances. We will have to see if this actually comes to fruition though, since much will depend on the unreliable motion of the already noted hard to forecast Cold Core Cut Off Low over the upper Midwest. The trend has been for decreasing rain chances through Friday after Monday, with little change in temperatures, although inland highs might not be quite as warm. I'm hedging toward keeping better rain chances for Tuesday at this point.


It appears that either solely South Florida or there and South Central will have the best chances of rain by next weekend, mostly showers with a deep , persistent onshore flow, thunder toward the west side.


There are no tropical threats with the two storms well out in the Atlantic. There is a trough now half way between the U.S. and Africa which could pick up Phillip, and Ophelia is having a  hard time with the TUTT low and high pressure north and ahead of it, which is creating shear winds against that system.    

Summer Like Rain/Thunder Chances Continue Through Monday

DESCRIPTION OF THIS IMAGE IS IN THE TEXT BELOW: Key features for the next few days are  a TuTT low SE of the Bahamas to lift NW-N, Closed Low over Lake Michigan/Illinois, High Pressure in the Western Atlantic East of the mid-Atlantic States , Strong Upper Low approaching the Pacific NW, and  the Southern Branch subtropical jet from the Baja to the Northern gulf, and lastly an area of low pressure in the Central Gulf (not shown above).  

SYNOPTIC SCALE PICTURE Through Monday (Above/Below): As noted yesterday, there is a weak area of elongated low pressure near/over the Bahamas. As expected, that region is circulating around strong high pressure to its north and east in the western Atlantic. Also of note is a strong TUTT (Tropical Upper Level Tropospheric Trough) to the east of  that area of low pressure and SE of Ophelia. Both features are tearing away at Opehilia. 


Meanwhile, the closed off Mid-Upper low complex continues near Lake Michigan and will continue in generally  over the same area until another system approaches the Pacific NW and Western Canada (blue arrows). Until that system moves east the low over the upper mid-West will remain in place. 

This is for the Monday time frame at the jet stream level or around 25,000 feet aloft. Again, we see the TUTT low circulation now east of Florida with the low STILL near Lake Michigan. Also, when looking toward Washington state, we see strong jet stream level wind pressing over the coast associated with the Pacific Express. These are supposed to continue east during early week and pick up that cut off low.  Meanwhile, note that trough (in black) lagging well behind to the WSW of the  low over Illinois. This trough will slide east and south through late week, thus, southern branch jet stream winds continue over the Gulf and increase a bit over the peninsula of Florida. 


Again, this is only in the upper levels. In the mid levels (not shown) is an inverted trough that extends from a weak low pressure circulation in the central Gulf and across Florida. That will be the key to the weather across the state through at least Monday.


TODAY'S ACTIVITIES: Today there is the area of elongated low pressure to the east of Florida. Showers/Storms are on the east side of the trough axis, far removed from the state. However, as far away as it may be, outflows from storms might need to be watched later today that might approach the coast, but not actually reach it. These could act as moisture convergence points for coastal regions to just offshore.


Otherwise, the main focus today for storms will be the elongated low-mid level trough axis extending from the Gulf of Mexico. This low pressure area is being enhanced by slight divergence aloft from the sub-tropical jet, although there is not a whole lot of storm activity associated with it at this point today. The areas to watch due to the presence of that boundary is the same area as the past two days, Gainesville toward Ocala and South toward Western Volusia/Flagler Counties, sinking south with time toward Sanford/Orlando and the Beachline. At the lower levels, the trough axis appears to actually be across the Beach Line corridor toward Tampa Bay.

The red lines denote trough axis' near the surface. Note the focal point across Lake County toward Volusia County. The other trough axis runs along the Gulf Stream off the Florida East Coast. The actual mid level feature discussed above is further to the east than this.

This can all be seen more easily by looking at the enhanced water vapor image, courtesy of weathertap.com (below):


Extensive drying in the mid-upper levels (in oranges) over the Panhandle in anticyclonic high pressure circulation is visible over the Panhandle with increased moisture further south over the peninsula. The gradient from drier to moist air is near the inverted trough axis. That gradient could serve to foster some stronger storms later today. There is a bit of a moisture squeeze play ahead of the TUTT low combined with the area of low pressure east of Florida, combined with an area of low pressure over the Central Gulf.  This will continue through Sunday and much of Monday for peninsular Florida.

The deepest moisture resides over  Southeast Florida, but plentiful enough moisture is available elsewhere. At this hour of 10AM, much of Central and North Central Florida remains stable due to the late night activity of yesterday. South Florida is already uncapped with showers forming along the SW coast and progressing slowly toward the ENE. Thus, earliest activity today will be over South Florida with showers and thunderstorms, some more lightning prone activity could form around Lake Okeechobee and drift through Palm Beach County and Martin County. Sea breeze convergence could occur over the Everglades and into Western Dade/Broward. Steering is from the WSW over this region south of the inverted trough, but is quite light at only around 10mph at most, so storm motions could be over come by outflows and sea breeze interactions making for chaotic storm motion once the area starts to fill in a bit. We'll also have to watch activity well to the east of the state, since outflows from that activity could converge toward the southeast coast, beginning toward SE Florida then progressing northward later today.

Quick Picture of what COULD evolve today: Thunder, mainly interior South Florida but working toward the east.  

Later activity toward North Florida but having much less motion close to the inverted trough axis where steering becomes light. Stronger winds aloft could generate more lightning prone storms, with outflows working south along either the west or east coast sea breezes, all within a weak cyclonic circulation surrounding the inverted trough in the mid-levels.

 All in all, the heaviest concentration of rainfall lasting latest should be over East Central Florida west of I-95 (much like yesterday) where the atmosphere is most capped this morning. Due to 'anticipated' later storm onset (in general), this area will have more time to destabilize through the length of peak heating as outflows from activity further north and south close in on that unstable zone just south of the trough axis. 

Storms appear most likely to reach the beaches over SE Florida and less so north of Vero Beach where steering is almost non-existent. Thus, the sea breeze collision over the far interior will not affect the coasts until that activity can send subsequently  propogating outflows toward the east  and against the prevailing sea breeze.  

As always at this time of faded summer, much depends today on which sea breeze (if either) is most dominant, or progresses inland the fastest inregard to where a collision  of both will occur. Using the 2-3 day rule (my personal one), today should end up much like yesterday over Central Florida as well as the area more toward the North, although it does not look like coastal Volusia/Flagler will see nearly as much activity at  or near the beach zones as was the case yesterday, or if so, not as early in the day . South Florida should see the biggest change today in regard to the amount of activity since it has been pretty quiet in this area the past several days. 


SUNDAY/MONDAY: These two days seem to be the ones that the immediate East Coast will actually get in on the storm activity, especially once the TUTT low moves north of the latitude of Central Florida which will allow a slightly stronger SW flow aloft to take hold. However, it will be an overall drier atmosphere by Monday, but sea breeze convergence should make up for that difference.


BEYOND: Finally the low over the Great Lakes gets the boot (or so it seems as of this morning based on model agreement and their trends). In doing so, the surface frontal feature washes out before reaching the state as high pressure builds in behind in. Thus, winds eventually amass a more ENE-E component at the lower levels. 


 <In regard to temperatures, there is no cold or cool air invasion. Just a modification as winds gain a more easterly component, meaning over night lows in the upper 70Fs near the coast and afternoon highs in the mid-upper 80Fs (in the interior).>


However, as noted in the top image there will be that lagging upper level trough,  thus winds well over ahead remain from the west. These winds could merge with the inverted trough axis later next week. This will be a 2-3 day metamorphosis during which time rain chances remain, but of more isolated nature. By late next though, the latest GFS has a bit of a deformation zone setting up across Central Florida which could result in increasing rain chances once again over Central and South Florida by Friday. Initially, the GFS showed the deepest moisture to be over South Central and South Florida, but the last two runs are  shifting the deeper moisture a bit more north to include Central Florida with the area along and north of I-4 still in the much drier air mass. Again though, older runs or more recent runs, this time frame is much too far out in time for confidence to be in either case  on the low side, realizing we are now talking about the end of the first week of October.


Time will tell. 

July Like Conditions Return On the First Day of Fall

Although anticrepuscular rays appear to converge onto a point opposite the sun, the convergence is actually an illusion. The rays are in fact (almost) parallel, and the apparent convergence is to the vanishing point at infinity.  Anticrepuscular rays are near-parallel, but appear to converge at the antisolar point because of linear perspective. Anticrepuscular rays are most frequently visible near sunrise or sunset. These were observed this morning, but were seen a few other mornings this week just before and during sunrise.

And at the same time as the above image, this storm was over the ocean. Looking toward Canaveral AFS, seaside.

TODAY: Today is the first full day of fall, as of 5:05AM. That might be true in regard to how the earth is aligned with, and rotating around, the sun; but the weather today looks much more like that characterized by a mid-July day. One with plentiful moisture and little to no synoptic scale boundaries. It won't be quite as hot as it is in July, but otherwise all things appear to be equal. And like in mid-summer, outlining any specifically higher potential areas for rainfall is difficult other than the blanket, all inclusive "all over the interior" stand-by.


As of 1pm , the sea breezes have begun per visible satellite imagery. Some showers were ignited earlier due to an outflow boundary off the NE coast in the Flagler County area which moved ashore in that region, but otherwise showers are few and far between. Moisture content today is high (2.00" +), and once moisture convergence begins as the sea breezes approach each other it will be even higher. Steering today is weak, but generally from the WSW-SW at 10mph or less, and apparently restricted to the north half of the state. Toward Lake Okeechobee and South into the Everglades currents are less than 5mph. Showers should start to begin well before the sea breezes meet, but most prolifically after 3:30-4pm. A few more lightning prone storms could form before and during that time, but have the greatest overall coverage and strength after 4pm -6pm.


Ocean showers were lacking this morning other than right over the coast of Central and North Brevard, since steering is no longer bringing them ashore north of Palm Beach County. A few formed within two hours of sunrise, and one was easily visible a full hour before sunrise as the first rays breached the horizon and lit the top of this tall shower under otherwise nearly full-dark conditions still in place while the moon and stars were quite visible even still...

Fairly uniform distribution of moisture and instability with weak steering, especially over the Southern 1/3 to 1/2 of the state. Further north toward Brevard, showers or storm debris could move offshore toward early evening, and perhaps a series of storms/outflows could back build to US1 after 5:30pm, and maybe move offshore north of the Beachline or just maybe as far south as Sebastian Inlet.

 Like most July days, the bulk of activity today will be over the interior, but visible from the coast albeit at a "not so far away' distance. It looks like there should be a good coverage of activity today, and like yesterday some storms could contain considerable amounts of dangerous lightning activity and very heavy rain. With slow storm motion, and with rains likely impacting some of the same areas impacted yesterday, localized street nuisance flooding/puddling is possible. Rains were quite heavy yesterday over the interior at some locations, and some areas received heavy rain more than once. 

Rain so heavy it looks 'bluish'. Note how lush the interior swamp lands are now after a full summer of storms.

Strong storms are not anticipated in regard to winds/hail, but if so would be most likely to occur toward the far north where slightly colder temperatures aloft might exist later today.. the strongest storms will likely occur due isolated/localized mesoscale boundary interactions.  


Storms/showers/remaining light rain pockets could continue in the chosen select areas until 10pm tonight, if not later. The rains today when all is said and done will favor more toward the east side of the state, but most anywhere 10-20 miles away from the immediate coasts could see rain today. The least likely area appears will be over the Western Panhandle, but there too, a strong storm or two could occur but of more isolated nature.

SATURDAY/SUNDAY: So far it appears nothing significant enough beyond what has been written for two days now has changed. Thus, more July like weather. Activity could start a bit earlier on Saturday...it is interesting to be watching this (below):

This area of disturbed weather  has no apparent surface lows, or any lows really although some guidance points to weak cyclonic circulations in the mid-upper levels here and there. Overall, this appears to be deep moisture being rotated around the western and southern periphery of high pressure that extends well out into the Atlantic.  The activity is propagating generally in the direction of the yellow arrows. Even though this is not a 'system', some of the moisture associated with this activity could come in to play over the weekend for at least the South half of the state.

 MONDAY/BEYOND: There is a nearly cutoff low pressure system, quite large, parked over Illinois. This area is quite expansive and Florida is just barely receiving some the mid level circulation around it (hence, the light WSW steering currents in the mid-levels). The surface front from it is almost completely wrapped around the low, but a weak lee side trough has popped up from time to time down the Appalachians, with a more well defined boundary tracking south then almost due west in the Southern Plains.


Most guidance has leaned toward filling the low and lifting it out toward the NE on Monday, while the frontal boundary gradually drops south and east with time into the far Deep South and into the Panhandle of Florida by Tuesday. At that point and beyond it becomes nearly indiscernible and dislocated from the parent low pressure area now very far away,  as nothing more than a gradual change in wind direction and atmospheric drying. 


Thus, by Monday rain chances might be restricted to the Southern Half of the state, but not entirely. There has consistently been a drying out period portrayed, but much will depend on where the boundary ends up over the state (assuming it washes out over the state). Wherever it ends up will end up being a focusing mechanism for moisture convergence so that despite lowered overall atmospheric moisture being infiltrated into the state due to the loss of the tropical connection, there could still be showers and thunder somewhere, apparently the whole way into next weekend. So far, Tuesday seems to be the most quiet day other than the far South and the Panhandle (where the front will reside at that time). The morning GFS of 2AM has the boundary washing out over Central Florida heading into mid-week next week as high pressure moves in to the north and easterly flow returns, but none of this looks particularly legit from a meteorlogically realistic aspect, so the future like all of them....heads toward:


"Live as if you were living already for the second time, and as if you acted the first time as wrong as you're about to act now"

Only Thing to "Fall' on Friday Will Be Raindrops

The Sun’s away

And the bird estranged;

The wind has dropped,

And the sky’s deranged;.....

This morning 9/22/2011 at sunrise

......Summer has stopped.

And some are very frustrated about seeing it go so fast. My sentiments exactly.

Grrrr...

Fall begins at 5:05 A.M. EDT, Friday morning. The autumnal equinox is defined as the point at which the Sun appears to cross the celestial equator from north to south. The word equinox means “equal night”: Night and day are about the same length of time. In addition to the near equal hours of daylight and darkness, the equinox is a time when the Sun’s apparent motion undergoes the most rapid change. Around the time of the equinox, variations in the position on the horizon where the Sun rises and sets can be noticed by alert observers from one day to the next. Eventually, it will be rising and setting along the southern horizons as we progress toward December 21-22 as the first day of the Winter Solstice approaches. 

TODAY: Deeper layer moisture is entering the picture as expected, although this still does not mean widespread rains due to lack of any boundaries and few triggers. Ample daytime heating though will give rise to  respectable upward motion (vertical velocities). The models are again a bit out of whack, with even the short term RUC rotating an  inverted mid-level trough from south to north during the day across South and Central Florida. This, in turn, would change steering currents from SSE to nearly SSW-SW by late today. Do not believe that will occur to such an extreme, but continued SSE-S Flow seems more likely, with winds closer to the ground remaining ESE-SE. This would progress the east coast sea breeze inland for the focusing mechanism for the peak storm period after 3-4pm west of I-95. If winds aloft do become more southerly, then outflow or even back building could work storms toward US1 north of Vero Beach by 5pm, to possibly the beaches from Daytona and north. Best hedged bet relies on storms remaining in the interior at this point though.

Up to this point this morning, it appears some showers with lightning from time to time generated from eddies off the western Bahamas,   worked into Palm Beach County. Since earlier this morning, they have been working up the east coast, with some renegade showers reaching the coast further north toward Flagler County. The showers seem to be increasing off shore now that the sun has risen. With that, perhaps the RUC has something there with the more SSE-S Flow to develop later in the day

 . 

But for now, it's probably best to rely on persistence, since there is nothing evident that would preclude a persistence forecast of past model trends. What is happening out in the Gulf is interesting though. It appears much of the activity there is being provoked by divergent Southern Branch jet stream winds...which will remain over the Gulf for at least 2 more days. These are shown further down in this post.

Showers along the East Coast should work north and possibly increase after 10AM. Some could contain lightning, more so after 11AM to noon. If so, outflow from these near the coast and just offshore combined with the prevalent ESE-SE flow at the surface will send boundaries inland for greater storm coverage. Storms could start to occur earlier today than in the past two days., possibly peaking between 3-5pm.

FRIDAY-SUNDAY: Not any change in line of thought for this time frame with an increased chance of thunderstorms   most anywhere. The pattern will eventually evolve as to end the morning rain showers near the coast or at least put a lid on the amount of them, with afternoon storms forming by early to mid-afternoon and ending near sunset. Storm motion will be slow, but they should work northward and  a bit toward the east, especially on Saturday and Sunday.

It was noted that a La Nina pattern was evolving or had evolved in August in a post over a week ago. What does that can mean as we work into winter? 

In regard to the tropics, tropical storms and hurricanes have hit Florida during La Nina events in October. So far, it looks unlikely to occur, at least through the first week of October. There has been, coincidentally since the La Nina Event was made public, a developing southern branch jet stream running across Southern California toward Florida...it is quite apparent still in model guidance..and is expected to remain in place to varying degrees over the Gulf and near Florida for quite some time to come.

 Here is the forecast for today's jet stream and the forecast of October 6  

 

A general  discussion concerning La Nina years follows.  Note that from these images above and then  provided below, that a La Nina like  pattern seems to already be established. It does not mean this will always be the pattern all the time, just the more prevalent one. 

.La Niña conditions returned in August 2011 due to the strengthening of negative sea surface temperature (SST) anomalies across the eastern half of the equatorial Pacific Ocean (Fig. 1). With the exception of the far westernmost Niño-4 region, all of the latest weekly Niño index values were –0.5oC or less . Also supporting the return of La Niña conditions was the strengthening of the below-average subsurface oceanic heat content anomaly in response to increased upwelling and further shoaling of the thermocline across the eastern Pacific Ocean

The better model performance, combined with the historical tendency for significant La Niña episodes (as in 2010-11) to be followed by relatively weaker La Niña episodes, leads to increased confidence that La Niña will persist into the winter. While it is not yet clear what the ultimate strength of this La Niña will be, La Niña conditions have returned and are expected to gradually strengthen and continue into the Northern Hemisphere winter 2011-12.

The Climate Prediction Center defines. . ."La Niña conditions" as existing when: A one-month negative sea surface temperature anomaly of -0.5C or less is observed in the Niño-3.4 region of the equatorial Pacific Ocean (5ºN-5ºS, 120ºW-170ºW) and an expectation that the 3-month Oceanic Niño Index (ONI) threshold will be met AND An atmospheric response typically associated with La Niña is observed over the equatorial Pacific Ocean Across the contiguous United States, temperature and precipitation impacts

associated with La Niña are expected to remain weak during the remainder of the Northern Hemisphere summer and early fall, and to generally strengthen during the late fall and winter. 

During September-November 2011, there is evidence that La Niña favors an increased chance of above-average temperatures across the mid-section of the country, and an increased chance of above-average precipitation across the Pacific Northwest

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html

La Niña episodes are associated with three prominent changes in the

wintertime atmospheric flow across the eastern North Pacific and North

America. The first is an amplification of the climatological mean wave

pattern and increased meridional flow across the continent and the eastern

North Pacific. The second is increased blocking activity over the high

latitudes of the eastern North Pacific. The third is a highly variable

strength of the jet stream over the eastern North Pacific, with the mean jet

position entering North America in the northwestern United States/

southwestern Canada.

Accompanying these conditions, large portions of central North America

experience increased storminess, increased precipitation, and an increased

frequency of significant cold-air outbreaks, while the southern states

experiences less storminess and precipitation. Also, there tends to be

considerable month-to-month variations in temperature, rainfall and

storminess across central North America during the winter and spring

seasons, in response to the more variable atmospheric circulation throughout

the period

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensocycle/nawinter.shtml

 

Will a 'Caribbean Express' on the Tropical Connection Dampen Weekend Plans?

Sunrise Sea Storm On The Approach This Tuesday Morning, Looking South-southeast from Cape Canaveral 

TODAY: Very little change in thinking required today through Wednesday. Mainly SE winds, light but prevailing from the surface to 10,000 feet over South and Central Florida continue to draw in sporadic atmospheric moisture globs. As anticipated, the east coast (namely Brevard and eventually parts of Volusia and Flagler) got in on the rain act over night through late morning. The Brevard Activity has ended, but not before sending outflow to the west through north, which is generating more activity further from the coastal communities toward I-95 and west.  Expecting most thunder and lightning over the interior today, isolated and possibly becoming a bit more scattered toward late afternoon and dinner time over the interior..mainly from Osceola County and north in the same locations as late yesterday, although more could be found toward I-10 as well. Some stronger storms are possible later today to the far north near Gainesville and west of JAX, although some high clouds on the approach from the west might offset that possibility.

It is up for debate as to whether the west coast sea breeze will be able to from today, or at least in regard to how far that breeze will work east and away from the coast. The pressure gradient at the surface is light through the lower levels, so with daytime heating it should be able to work a good  10 -15 miles inland. The East Coast Sea breeze has started already, but should make less inland progress north of Volusia County. Stronger storms are possible over far North Florida and perhaps toward the SW Coast. 

TONIGHT/WEDNESDAY: Increasing moisture on continuing SE winds (light and variable at the surface overnight) should continue. The diurnal cooling of the land mass overnight in opposition with the now warmest waters most of the east coast sees at this time of year could give rise to more showers and maybe some thunder after midnight, mainly upstream of the North and Central Bahamas where wind current eddies provoke/stir the atmosphere over the warm waters to generate showers. This morning the 'chosen spot' was  eastern Brevard County. Guidance points toward that location again, but the reality is that there is no definitive way to know for sure if there or anywhere will fall victim. My location received over 1.8" of rain between 1AM -11AM this morning.

Downpour around 9:30AM, Accompanied by Thunder

 
THURSDAY/WEEKEND: Will put this entire frame in one category for the time being.
The frontal boundary alluded to yesterday near the Mississippi River, sure enough as guessed (despite what some guidance had shown), is now no longer forecast to progress beyond NW Florida toward NE Florida for quite some time to come. The parent upper level low is shown by the GFS to nearly cut-off from the main jet stream flow..although in doing so over Lake Superior, it is resupplied by impulses from the Northern Branch Jet Stream from the WNW (Canada)...these impulses or waves of energy evoke the low to Drop toward the SSE over Lake Michigan as the are pulled in and drop down the backside of the low. 


Despite the normal attempts to continue eastward it begins to confront the vast high pressure area that stretches from the far Eastern Atlantic to the United States.  If one is to believe the GFS, this trough is no match for such a might region of high pressure, so instead of moving further east it simply works south with time...with each disturbance feeding in from the back (west)...it drops yet further south through the Tennessee Valley. As such, the pressure gradient in the mid-upper levels tightens harboring more of a steady SSW flow aloft, while winds at the surface remain much lighter, enough to allow sea breezes each day.  


Meanwhile, as the trough/low drops further south, the "Caribbean Moisture Express" is enhanced further both from the far SW Gulf as well as the south and Central Caribbean.  If again, one is to believe the GFS, then this moisture will feed the whole way up the Eastern Seaboard over  Appalachians toward Maine through Monday next week as a series of impulses exits Florida (perhaps as a result of diurnal afternoon thunderstorm activity over the state) or off the coast of SE Georgia, all commencing sometime around Thursday but much more pronouncedly by Saturday.

Colors are depicting the amount of deep layer moisture. Purple is very high moisture content (necessary to produce rain) whereas the light blue toward the Rockies is very low. This is the forecast of the GFS for Sunday evening. But it continues through early next week. Moisture is being converged or squeezed between high pressure on the far right and low pressure to the west. In this image is also shown some higher moisture dropping into Louisiana/Eastern Texas. That is a reflection of another disturbance dropping south, to eventually join forces with the "Tropical Connection Train" by Tuesday.

 Again, the extended as always is to speak in only very general terms. The next model run will show a variation of this theme...and by the end of the weekend if not much sooner the picture could be quite different. In fact, there might be several variations or completely different conclusions on a continuing basis. The truth can only be revealed as it happens, or at least within a 24-48 time frame. 


 It would not surprise me if even a surface low forms over or near Florida during the course of the weekend. There is  a brief time frame where Florida is shown to be in northerly winds, as perhaps one indeed does form, but then gets scooted up the east coast as some sort of faux warm front.


Flooding might become a big concern for eastern parts of the Mid-Atlantic and west toward Eastern Tennessee and into Virginia before all is said and done if the scenario depicted this morning actually unfolds and comes to fruition.


TROPICS: The tropics are being watched, and there might be an "Ophelia" on the approach in the next couple of days. At this point, it appears any said such storm would have to be either diverted north or continue westward into the Caribbean...and over the Leeward/Windward Islands. If it is diverted north, that would mean a break in the pattern just described above...and anything beyond Monday is completely out-to-lunch on the GFS run of 8AM this morning. 

The rains finally broke this morning

Slow Transition to Moisture Laden Southeast Flow Emerging Through Wednesday

A slightly better chance of thunderstorms today toward Ocala and interior Volusia/Flagler and in the Gainesville area. Also along the SW Coast. Coast showers could re-appear within 1 hour of sunset (very isolated) along the Central to Southeast Coast...more numerous the NE Coast toward JAX and SE Georgia.

TODAY: Not much change in the line of thinking from yesterday's post. An inverted trough has appeared, temporarily as almost a very weak close surface low over Brevard County. This feature will move inland with the sea breeze and daytime heating as a weakly defined, inverted thermal trough to act as a focal point for more thunderstorms than the past few days over the interior (which isn't saying much). Lightning was observed near noon time in North Brevard as the showers, moving generally toward the NNW moved inland from Central Brevard.  There is a small chance of an isolated shower or two re-appearing within one hour of sunset along the beaches most anywhere while the activity over the interior should dwindle rapidly after sunset. Northeast Florida seems the most likely candidate for that early evening activity, although one or two is possible Central.


TUESDAY: Another slice and dice day of where/when the renegade showers will occur. Most likely before 11AM along the east coast, progressing into the interior by shortly after noontime and re-emerging as thunderstorms from early afternoon, and peaking in strength between 4:30-7pm. in other words, much like today.


WEDNESDAY and Beyond: The NAM has been consistent (for a change) at showing a region of higher moisture (PWAT) air over the SW Atlantic to progress WNW toward Florida during the course of the next 48 hours. For two consecutive runs one can actually trace the rain field areas it depicts approaching systematically toward the east coast of Florida for arrival by late Wednesday afternoon. The GFS is far less as obvious, but both do show a broader coverage of atmospheric moisture for a greater coverage of showers and some thunderstorms, but by no means will every one be seeing rain. All in all, it might seem more like a typical summer day albeit just a tad cooler by a few degrees. Favoring the west side late in the day for the heavier storm activity. Thursday looks similar.


Elsewhere, during the next few days a frontal boundary will be inching eastward toward the State. It is moving at such a snail's pace as it rams into the ridge running down the Appalachians as noted in the image above (with yet more in the Atlantic)..that it can barely reach Central Florida before being stretched thin (Saturday/Sunday time frame).  For comparison's sake, were this a 'normal' frontal boundary in mid-winter it would be through the state by Tuesday night from its current location, which is  down the Mississippi River Valley area.  It still appears the boundary will make it to Central Florida or thereabouts, and be able not to progress much further. That is at the surface. Just above the surface the upper level supporting trough lags well behind..as if to emphasize this is not a 'big temperature dropper', but rather a focal point for showers/thunder.


Beyond Saturday we are already into the time frame of greater unreliability and tremendous variations from run to run, although the GFS has been fairly consistent in having this boundary merge with a broad area of low pressure over the Caribbean.  In fact, the morning run now cuts the remaining frontal boundary off into a close surface to upper level low pressure area encompassing most all of Florida by the middle portions of next week. This is highly unlikely as well as any other extended outlook has and ever will be. But the implications, or rather, the tendency for this model to want to evolve into some sort of transformation of low pressure areas off and on again for over a week near or over Florida in the extended can't be completely ignored. There is a brief drying period during the transformation, but the gist has been that no big temperature dropping frontal systems appears yet to be fully in the making for a big cool off for anywhere beyond the Panhandle and Northern portions of the state into October. That too, could change. But not within the next week when fall begins on September 22nd at 5:05AM. Last year, our first fall like day arrived almost simultaneously with the passage of Tropical Storm Nicole (September 31st). From October 1st and beyond, summer or any semblance of summer ceased to exist.

Persistent Current Patter Remains In Place Through Tuesday

Sunday morning rain-shower near the Coast of North Brevard County. This shower seemed to form along the leading edge of wind surge, which never quite made it beyond the immediate coast...and after which retreated to offshore. This could be the chain of events that unfolds the next two or three mornings, which an enhanced area of more prolonged rainfall somewhere between Coastal North Brevard toward St. Augustine each day during that time frame.

General Area of Rain shower activity today (mostly isolated), except possibly along the coast from North Brevard, through Volusia, and into Flagler County where there is potential for some higher rainfall totals. Little change in the current pattern is expected through Tuesday.

TODAY-TUESDAY: Little change in the overall pattern appears to be in order for the next 48-72 hours. Weak low pressure that formed near the Carolina Coast slid NNE ward during the past 24 hours and has left a remnant mid-level boundary just off the SE U.S. coast. 


Yesterday, the end of that boundary reached into the JAX area, whereas this morning the boundary had pushed south toward Daytona as high pressure built down the Appalachians. It is that boundary which will be the prime instigator for potential more coastal rain events due to the fact that this thinly stretched out boundary cannot progress further east due to a vast high pressure area extending completely across the Atlantic to the coast of Africa and southern portions of Europe.  It is possible that heavy rain fall events could occur in the next 48 hours somewhere along coastal North Central to Northeast Florida from overnight to early morning and one or more of these days. Meanwhile, a frontal boundary will be inching in from the west (now across the Southern and Central Plains)...but the log jam will be hard to break. Thus, little change for a while until 'something gives'.


The weather today is a far cry from what occurred on this date in 1926 (85 years ago), the year of the Great Miami Hurricane. Even as little as 24 hours prior to that storm, hurricane warnings were not hoisted. 


I will add that there is also a secondary bubble of high pressure over the SE States center just NNW of Florida. This appears to have broken off from the fixture that was over Texas most of this year (since early mid-spring time) which generate the drought there. That high pressure is almost completely gone for now, but an even large high pressure dome could be in the making for much of the Western U.S. during the week ahead. It was the leading (and in sinking( side of that high pressure that was responsible for the string of dry days over Florida last week. That high pressure will gradually flatten out with time, with a portion eventually  ejecting eastward into the Atlantic with the other portion retrograding into the NW Gulf and back into Texas. This process will be a slow one though.

Did you hear about the big rainfall totals overnight Friday night into early Saturday near Jacksonville? Here is a Storm Total (of rainfall) obtained via weathertap.com compiled from the JAX radar yesterday morning, followed by a preliminary informational statement release by that office. This was Day 1 evidence of that boundary at play. 

"A FRONT STALLED OUT OVER THE AREA COUPLED
WITH A MID LEVEL DISTURBANCE HELPED PRODUCE STRONG STORMS WITH
HEAVY RAIN ACROSS A PORTION OF THE JAX METRO AREA. 3.35 INCHES OF
RAIN WAS REPORTED AT CRAIG FIELD OVERNITE. HOWEVER...THERE HAVE
BEEN DOPPLER ESTIMATES OF NEARLY 10 INCHES NEAR JAX AND PONTE VEDRA
BEACH. MAJOR FLOODING WITH UP TO 3 FEET OF STANDING WATER AT JAX BCH
AND 6 INCHES OF STANDING WATER IN A CLUB NEAR ARLINGTON.
DOPPLER RADAR CONTINUES TO INDICATE CONVERGENT BANDS OF SHOWERS...
SOME HEAVY...ALONG THE COAST" - JAX (Jacksonville NWS Office)

Meanwhile, this morning the same sort of event occurred in Volusia County, although not nearly to such a degree. It appears it might not be over quite yet, even though as of this time the rain there has ended, more lurks very close to the coast if not already back on shore as I type. I've noted an area of interest in lavender where more convergent rain-bands could set up today or tonight in the first image.


Elsewhere, despite model guidance and actual 'near current' data portraying dry conditions over South Florida, rain showers moved into Palm Beach County..much to everyone's surprise. These are low topped showers, but nonetheless persistent. These showers appeared yesterday morning and once again this morning despite lack of rock hard evidence that would call for them to be placed in a forecast due to lack of any sufficient surface features other than some moisture.  There appears to be a small cyclonic circulation approaching far SE Florida as of noon time, so more showers could move into Dade/Broward Counties, and after a break toward the Keys, they might be in for more later today and tonight as well.


Otherwise, when looking at parameters to support thunderstorms, the most unstable atmosphere has been along the east coast of Central Florida mainly from Central Volusia to Central Indian River Counties. Despite these parameters that are based on low level factors, the mid-levels are too dry to support anything other than low topped showers in the absence of a triggering mechanism other than convergence which happens rather sporadically and haphazardly. Only closer to the near 'phantom boundary' near Volusia/Flagler where moisture is deeper through a greater extent of the atmosphere does it appear more certain that rain chances should  be higher, as well as some thunder. Even an offshore waterspout should not be counted out. A YouTube friend of mine shared that he saw a waterspout offshore South Brevard Saturday morning, but this was not noted in official documentation released from MLB.


MONDAY/TUESDAY: As it appears now, little will change in the given on again/off again pattern until a deeper, stronger  trough can approach from the west   toward the state to nudge high pressure out of the way.  I will write that this was originally portrayed to occur (several days ago) in full by Saturday, then Sunday..but it keeps being pushed further out in time. Thus, although a BIG change is expected to transition through on Wednesday and be in full affect by Thursday..we'll just have to keep monitoring. It is the time of year for the first cold front to reach Central Florida, so this train of reasoning is not out of the question.


BEYOND: With the above already stated, one can make the assumption (and if 'reading' the models, it would be a fact)..that by Thursday the mean moisture advection will commence from the SouthWestern Atlantic and even the northern Caribbean. This would bring forth even deeper atmospheric moisture and a return to thunderstorms, especially by late Wednesday and more so on Thursday through Saturday. That is the course of thought as of this morning, but it will take two more model runs (or by tomorrow morning) for this to be more assured.  In the great beyond, a combination of the front (trough) from the continent is depicted to merge with moist/cyclonic (low pressure) circulation from the Caribbean over Florida, at which point the GFS looses credibility completely. The over all trend though, is increased rain chances on Wednesday as thunder storms become more likely (or in other terms, beyond occurring in only random/isolated fashion).

Sunday Morning, September 18, 2011