"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".

Thursday, July 28, 2011

Near Zero Rain Chances Through Saturday as Don "Not so Juan" Moves toward SE Texas

THE RED LINE is the axis of low upper level pressures (TUTT) now exiting toward the West of Florida. This was located East of the state on Wednesday and brought the high clouds in. Much drier mid-level air follows in its wake off the Atlantic today as one can see by looking outside. See text in caption for more details.
This drier air is just now moving into all of North Central Florida today. Otherwise, in regard to Tropical Storm Don, the winds associated with this TUTT are forecast to increase over the Gulf as they merge with the strong, drought producing high pressure over Texas in the next 24 hours.  There is another TUTT over NE Mexico, with increased shear ahead of Don, especially if it moves toward far SE Texas (South of Corpus Christi).
TODAY: The trough that brought all the clouds to Florida has obviously moved on to the west as an open 'wave'. Obviously in that all of those high clouds are now absent. Wind shear with this system is creating cloudiness now way west of the state. The blue line and circles above shows where these winds are now located per latest analysis. These winds should increase in the next 24-48 hours as they combine with a large area of high pressure building SE ward toward Florida from the South Central Plains. Florida will be encompassed by the Dreaded Drought High Pressure of Texas Fame on Friday and Saturday (for the most part).

LOCALLY: Another day in which I've completely disregard each and every model for today. They all seem to have over-estimated the amount of moisture available in the mid -levels. Latest analysis indicates that there is still high PWAT air, but it is mostly contained at the lowest levels with just a bit in the upper levels. This leaves at vast mid-level dry layer which only the area in Eastern Volusia County could utilize (of what moisture remains there) to create showers along the sea breeze before this air starts to pull out to the WNW. I have not seen that any lightning has been associated with the showers in Volusia as of noon time, but there is still a small chance of such..mainly toward SW Flagler County.
Otherwise, showers are showing up on radar and satellite imagery over the Atlantic, but likely will not make it across the "cooler" waters of the near shore Atlantic waters off the Space Coast from whence they generated further to the east. Further south, the air is almost just to plain dry to support showers, although there could be some showers that will move onshore south of St. Lucie County toward sunset in to Dade County where the Gulf Stream waters are much closer to the coast.  Best chance of thunder and showers during mid-afternoon through early evening are noted as drawn in with my Crayolas.

In this image we see DON in the lower left. Don is moving toward the WNW. Remember, there is the shearing winds aloft approaching this system as shown in the first image.  Additionally, there is shearing winds to the WSW of where Don is currently vectored toward.  Showers and some thunder today as shown by the chosen crayon colors. Best bet seems to be on the West Side of Ocala toward Gainesville and west of the St John's River Valley up toward I-10 later today. There is also a chance of a storm near Tampa Bay, but very isolated. The dry mid level air has worked into the area, but if the layer of dry air is not too deep a storm or two could form there with mainly showery type activity elsewhere along the SW Florida Coast.

FRIDAY-SATURDAY: This looks to be the all in all driest period for the state, save for NW Florida. Higher humidity and persistent onshore winds will make overnight lows warm at the beaches and hot over the far interior toward the West Side of the State during the afternoons.

SUNDAY-MONDAY: The mid and upper level dome of high pressure centered over North Central Texas will continue to stretch across the SE States, including Florida. Most of the moisture will pocket across the Panhandle Region but begin to creep into NW Portions of North Central Florida later on Sunday, as a trough at the mid-levels (as advertised in previous posts), begins to dig down the Appalachian Chain, perhaps abetted by their altitude and the lee side trough created by them at the lower levels. By Monday, the Texas Death Ridge will break down with the surface Atlantic Ridge and the mid-level ridge from that area as well over Central Florida. With that in mind, storms should be able to generate mostly north and south of the ridge, favoring North-NW Florida south and eastward to Volusia County, and South Central/South Florida (activity enhanced by Lake Okeechobee in that direction). Rain chances, in other words, go up for all but coastal Southern Volusia through Coastal St. Lucie County.

TUESDAY: Surface ridge axis across South Central and mid-Level Ridge axis around South Florida with a cooler aloft WNW-NW steering flow could harbor  some stronger thunderstorms to port along the East side of the state. But will all of this new found 'troughiness" be too much? This is unusual to have a trough this far south this time of year. And as such, rather than leaving things be (and was feared might occur)...the GFS is now showing that by...

WEDNESDAY: An area of low pressure in the low-mid levels begins to circulate over Central and South Central Florida in a pool of moisture. This could mean that Wednesday will end up showery or stormy. But so far, it's looking more toward the showery side as this will be a bit of a modified tropical entity, temperatures aloft will be warmer. We'll just have to wait and see if this does indeed occur. Additionally, there is a tropical wave well out in the Atlantic that so far appears will cross the Lesser Antilles and easily move into Cuba, perhaps the Southern Bahamas. I think it is at this point the GFS is completely confused with how to handle the two conflicting synoptic scale scenarios..Will the tropics win out and place Florida in Tropical Moisture from whatever becomes of the wave, or two: Will the land mass type frontal boundary win out, leaving a scenario favorable for afternoon thunderstorms to continue. Only time will tell...

TROPICS: Tropical Storm Don Juan not looking so sexy right now. Shear is now approaching the storm, but might take another 24 hours to get there. Thus, Don could increase in strength today, but very well could weaken as it approaches landfall somewhere near Rockport, Texas (is my guess)...north of Corpus Christi. There is also shear AHEAD of the system over NE Mexico which is expected to persist. Don is a very small storm, so there is some argument that it could do just about anything. However, it doesn't really appear to be organized enough to do much more than increase in strength today before more shear moves in over night tonight. Note that all of the storm force winds are in the NE quadrant..with very little toward the SW Side. Never say never. I would not expect Don to be anything more than a Storm at landfall. Unfortunately, because of its small size (at least as forecast), it will do little to nothing to appease the drought over West Central Texas. The Dallas area toward Houston might fare much better though in that regard. The biggest hassle from this system will be localized heavy rainfalls and perhaps some tornado watches over SE portions of coastal Texas as the storm approaches the coast. Otherwise, there could be some higher rainfall totals indirectly related to the storm itself; that is, from moisture transport into areas that area very dry. These areas will not hold new found heavy rainfall very accommodating , having a hard time for the dry soils to soak the rains in.

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