"But seeing they could not See; hearing they could not Hear"
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"From its chamber comes the whirlwind, and cold from the scattering winds." - Job 37:9.

"The wind blows to the south and turns to the north; round and round it goes, ever returning on its course".

Saturday, September 24, 2011

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 (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. 

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