"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, October 2, 2010

Summer ("OFF) - Fall ("ON")

(Image: low pressure center near or over the Cape mid-morning this Satur-day)
SYNOPSIS: Who flicked the switch on October 1st!? Just stick your toes outside and feel the difference in the air mass out there which began yesterday. Low and mid level low pressure contained within a large, deep upper level trough which extends along the entire U.S. East Coast is located very close to the Space Center mid-morning. Image included in this post shows the moisture trying to wrap around this low with some enhanced cumulus showing up on recent visible satellite imagery to the north of the Space Center which is visible with the naked eye from Canaveral. Meanwhile, a short-wave trough/upper level vorticity max is rotating around the more prevalent upper level trough and is bottoming out near the NW Keys (where some isolated showers have popped over the waters NW-N of Key West). This vort max will translate NEward in the upper level trough and pass across south and central Florida this afternoon and evening. A few rain showers exist off the N. Brevard Coast and points north to meeting land near Jacksonville.
TODAY: Beautiful morning to start the day, with a 7AM surface observation at the Port Entrance reading 70F degrees and a dew point of 70 degrees as well with light/variable winds. This would reflect this area being near the center of the low shown in the included image. With light winds and drier air in surrounding areas, temperatures will quickly rise thru late morning into the afternoon, especially away from the coast toward Orlando.  As noted above, an area of upper level energy is passing near the Keys this morning. This area is about to reach the base of the upper level trough and from this point on will translate NEward during the day across South Florida and across South Central Florida this afternoon. As it crosses the depicted low the resultant coalition will (1): strengthen the low to a small degree, and (2) Begin to lift the low off to the NNE and away from the state. As it lifts north and pulls away from the state drier air will be advected down the state, mainly across North and Central Florida in the form of a 'dry front'. But as far as the weather goes today...
Current analysis shows highest dew points and mid-level moisture, enough to support rain showers, are playing a gambling game with the immediate east coast from near Patrick AFB - Jacksonville, more so once one gets south of the North Brevard County border where it's very touch-n-go. Light winds this morning should eventually become NNE by noon time as the low shifts slowly away from the coast. In doing so, some richer atmospheric mid-level moisture will be advected around the backside of the low into North and perhaps Central Brevard County and all points north to near St. Augustine. At the same time, the pocket of upper level energy will begin to pass over head, with its first heralding been made around the 1-2pm time frame in the form of increased near shore showers mainly north of the Cape. As we work into mid-late afternoon some of these showers will advect south along the coast and possibly reach as far south as Patrick AFB, at the most, in the more prevalent NNE flow which would affect the areas mainly along and east of I-95 before passing offshore near South Brevard. The Weather Channel and the SPC (Storm Prediction Center) are showing a slight chance of thundershowers this morning for the east coast this afternoon and evening, but I do not believe this will occur, but if it does it will be over Volusia / Flagler County. Meanwhile, across South Florida from near West Palm Beach and south other isolated rain showers could form by early afternoon with heating of the day in widely scattered fashion which will move off to the east or ENE and off the east coast as the upper level energy passes overhead that area. Just in noting though, should the area of low pressure depart the coast earlier in the day the chance of rain will go to pretty much zero this afternoon for East Central Florida.
TONIGHT: Chance of an isolated shower continues from near Cape Canaveral and points north after dark with South Florida clearing out due to departing upper level energy and loss of daytime heating, combined with drier air impinging on this area first. Again, these showers will be very widely scattered if they do exist at all over the land mass, so most everyone will be dry. If it does rain anywhere today or tonight, it will be brief.
MONDAY-TUESDAY: "Dry Front" passes through. Temperatures inland will be cooler mainly because of the drier air in place and not so much due to cold air advection as one would expect in a  true FROPA (frontal passage). Drier air and northerly winds will permit high temperatures inland to reach the mid-80s with lower 80s along the immediate coastal communities. On the synoptic scale, upper level trough will remain over or just to the east of Florida with the mid-level low cutting off near Tennessee. This low will move ENEward during late weekend into early next week and impact the NE states with more rain and wind, somewhere around Pennsylvania-Virginia-New York look to be the most impacted at this time. As this low moves out and weakens high pressure bridges east across the Mid-Atlantic States from the Central Plains while low pressure persists over the Caribbean eastward toward Puerto Rico.
Meanwhile, another reinforcing front will be passing across the Central States and enter the Deep South. This front will be the clincher as far as temperatures go for Central Florida by midweek, since it currently appears it might become stationary over Central Florida as it meets the boundary delineated by the lower pressures over the Caribbean. As such, the forecast for Wednesday and beyond becomes a little sketchy, although the impacts for Central and South Central Florida temperature wise appear to be pretty minor either way.
WEDNESDAY-FRIDAY: What will become northwest-north winds tomorrow will veer more toward the NNE-NE by late Monday and eventually NE-ENE along the coast on Wednesday. This will be a long fetch surface flow, and as such rip currents will become an issue as seas offshore become somewhat rough and winds become breezy at times due to the low pressure to the south and high pressure to the north across the entire state. As this flow persists shallow moisture will be advected across the state with an ever increasing chance of low topped showers to develop well offshore which would traverse across much of the state, mainly south of a St. Augustine-Cedar Key line. With such persistent NE-ENE flow in place, temperatures will vary little and begin to modify toward a norm 'central point' especially along the coast, where lows will be in the low 70s with highs near 80 (plus or minus two degrees). In other words, little variability between over night lows and daytime highs, most notable at the coast.
Exactly how long this pattern will persist is almost beyond the scope of reason, so in other words...not expecting much change locally for quite sometime beyond late Wednesday. However, further south toward Homestead and the Florida Keys moisture associated with the broad area of low pressure over the Caribbean might be able to creep northward beginning late Monday or Tuesday, and thus increase the chance of showers or perhaps even some thunder down there by mid-late week.
TROPICS: Invest 97L has been designated by the NHC (National Hurricane Center) and is located over a relatively broad west-east oriented region east of Puerto Rico. Elsewhere, and as one would expect per the discussion above, the Caribbean is being ogled with little affection toward tropical development. Actually, the chance of development there is pretty much zero during the next 48 hours. It appears that invest 97L has two options, either (1) strengthen into a tropical system, perhaps an Otto, which could play games with the forecast for the Southeast Bahamas but pose no threat to the U.S. East Coast; or (2) continue moving west or westnorthwest and never strengthen. Either way, Puerto Rico, the Dominican Republic, and the southeast Bahamas will see an increase in rains and gusty winds associated with them from time to time at a bare minimum.
So are we done with Tropical Concerns for the 2010 Season? Not necessarily so. A shift in the current pattern, which at this time is actually increasing in its complacency this morning will eventually come to an end, but this could take a good 2 weeks to do so. Expect the activity in the Caribbean to persist for quite sometime, and perhaps shift a bet west toward the Yucatan. Development down there could still impact the SE U.S. states later down the line. Hurricane season officially ends November 30th. Climatology shows that in late October storms have formed mostly from the Dominican Republic northwestward to off the Florida East Coast as well as in the SW Caribbean near the Yucatan peninsula, although storms have formed in all areas in between these zones as well.

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