"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 14, 2011

Chance of Heavy Lightning Storms East Interior Late This Afternoon

Developing situation at 1pm. West coast sea breeze and showers with some lightning is progressing eastward. Believe it will slow down during peak heating. Otherwise, storms on the east side could start in full by 3pm. Thus, timing on rain chances could be deemed too late in the test below. But, believe the west coast sea breeze will slow down a little over the interior. Meanwhile, very weak seabreeze is forming over portions of SE Florida very slowly and working north. And most importantly for today, the outer barrier island of A1A/Brevard is developing a more southerly wind. This should increase in strength ALONG THE INTRACOASTAL after 4:30pm...setting the stage for the remainder of the day/evening. Otherwise, inverted heat troughs along the east coast should set up between I-95/US1 or even US1/A1A (more likely north of Vero Beach).

SET UP FOR TODAY: Actually, not a whole lot different from yesterday. The main difference is that the stationary/cold front over the Deep South is slowly sinking south and will become a much bigger player in the forecasts for Friday and Saturday. Also, the bane of South Florida's existence, the surface ridge, has sunk south toward the Florida Straits adding an further twist to the equation.  Otherwise, weak sea breeze is established way out in no-man's land (barrier islands) which I expect, as it always does, will turn almost due south and strengthen after 4:30pm. This is realized more along the river ways than at the beach oddly enough. The sea breeze elsewhere will remain light and very shallow in vertical depth, with light west to east steering across the South Half of the state and just a bit from the WNW over the North Half. Everything becomes increasingly convoluted over far East Central Florida as usual..caught between a rock and a hard place it seems all the time. Note comments on the above graphic. Once again, dead Central is the LEAST likely to have early afternoon storms beyond a rain shower as noted below (see the comments)

SOUTH FLORIDA: The area near Lake Okeechobee to Miami is under a completely different regime than further north, although most areas will rely on moisture convergence being forced upward to generate storms in the absence of any triggering mechanisms either way. The air mass is more dry over South Florida today than yesterday, but not THAT dry. Rain showers are getting a later start, but should become a bit more numerous by mid afternoon. Some thunderstorms could form along either sea breeze and merge first in Palm Beach toward Martin County with the Lake O breeze. The bay area around Key Biscayne might also be a hot trigger spot where deep moisture convergence is already at hand. Outflows from this activity will set the domino tiles in motion for further development, but believe any thunder down in South Florida today will be a bit more isolated than in days past due to warmer air aloft than the past two days. Most likely areas are in orange (but not exclusively so).

NORTH FLORIDA: Closer to the stationary boundary and a mid level trough axis running along I-10. Both early and late activity possible, the latter being the strongest. This activity will include St. Augustine, Flagler County, and possibly Central or only Northern Volusia County, but probably not all THAT strong.

CENTRAL FLORIDA: Same as yesterday, only different. In the case of yesterday, South Florida was the more unstable by far, and activity there  started in Martin County worked very very quickly into St. Lucie, then Indian River, then South Brevard Counties like clockwork and as anticipated in the post. Outflow worked right up the sea breeze (which was close to the coast the further north one went)  and triggered more activity along the west bank of the Indian River toward Titusville due to the enhanced river breeze combined with outflows from the south.

In the case of today, North Florida is more unstable and has more moisture. Thus, more shower and storm activity is expected here. More rains, more outflow, and south it will go into Southern Volusia toward North Brevard. Meanwhile, some activity might try to work north from Indian River County as well due to a Lake Breeze induced storm near Martin County.  

In the meantime, the sea breeze proper should remain very light other than out on the barrier island strip, while the upwind intracoastal will be even stronger. With time, this wind could work into far North Brevard toward Oak Hill, depending on long it can last before interrupted by incoming convective showers of appreciable depth and how strong it actually becomes. 

The two different storm genres of North Florida and far North Central should begin to merge...but any true to life  sea breeze activity could start up by 4:30pm.  Today's forecast was based on the assumption that the intracoastal wind machine will interact with the Orlando Heat Island from 5:30pm thru 7:30pm. There could be some pretty good storm coverage over East Central Florida 'somewhere' west of I95 if things materialize as envisioned. Otherwise, it could be just another day like yesterday.  The reason for why I think it might have more coverage is due to another factor.

There is a TUTT low (upper level) passing west of Cuba today. An inverted upper level trough axis could very well be extending NE from the low (the NE quadrant aloft). Along this trough, which is near the jet stream level, there would be divergence aloft. This would be the 'star' factor for more coverage today than yesterday because divergence aloft bodes for rising air currents below. Sort of like holding a tube of toothpaste upright, taking the top off, and squeezeing from the bottom up.  
To paste coming out the top is your thunderstorm.  The harder one squeezes, the more paste you get. But how hard will the 'squeeze play' be today?  Otherwise, the atmosphere if pretty much the same. Well, that, and temperatures aloft are just a degree or two cooler than yesterday...SUPPOSEDLY based on morning soundings from Tampa and KSC. However, those soundings this morning might have been taken at a time when a cool pocket was passing overhead; too hard to say 'for sure'.


STORMS TODAY COULD BE: Under the assumption there will be more coverage, as the saying goes, "The more the merrier". And in this case, the more outflows boundaries and drier air aloft, the merrier the lightning maker will be. Would not be surprised to hear a statement for excessive lightning be made around 6pm tonight somewhere west of I-95 in the area noted below.  The other factor today would be excessive rainfall over the interior. More areas that are very close to cloud to ground lightning will likely experience some bigger rainfall totals. But why? Lightning is often triggered during the peak updraft phase of the storm and as the down draft begins in full. Storms will move very little if at all today over the interior..especially after 7pm as storms most everywhere become predominantly downdraft ridden. Thus, if one is near the lightning, they are also near the eventual downdraft filled with 'water'.   Could be some stronger wind gusts in the initial down 
pouring of rains from any storm because the air aloft is a little drier today. Drier air cools more efficiently, and cooler air rushes to the ground faster, and the faster it rushes to the ground..the stronger it expands outward upon reaching the ground.

ACTIVITY SHOULD END fairly rapidly after 7:40pm and be reduced to dwindling light rain by 9pm where the greatest concentration of outflows eventually ends up over the interior. Winds aloft from the east should clear out the anvil debris to the west and allow the remaining clouds to dissipate rapidly toward midnight.

FRIDAY: Different set up. We'll deal with tomorrow when it comes. The stationary boundary will be sinking further south. The plot thickens.

WEEKEND: Good luck with this one. The GFS was very good with calling for a backdoor cold front to enter the picture this weekend. Remember, this was first mentioned in a post over a week ago. The only difference now is two fold 1) will a weak surface low form well east of Florida or Georgia with the boundary going stationary somewhere just east of Florida?; or 2) will it move on in to Florida and wash out over the state as some sort of inverted trough near the east coast...setting up for some bigger rain chances as soon as earlier in the day on Saturday? Playing it by ear for now. The jury is still deliberating, and not ready to call the liar's bluff.

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