SYNOPSIS: The large upper low over Illinois is slowly moving toward the east to ENE today but will make little progress. Meanwhile, there appears to be a mid-level trough axis running down the east side of the State this morning, and latest RUC forecast shows very little displacement of it during heating of the day, likely due to a thermal low level trough being established across the interior with heating of the day down the spine of the state. The deepest moisture is along the east coast from Brevard and south. South Florida had the most moisture this morning, but it appears as though since the time of their sounding at 8AM it could have lowered further. In all, the deep moisture of days past is moving out along with yesterday's cloud cover.
The large low over the upper MidWest will move east to ENE through Thursday as a series of vort lobes and surface boundaries continue to dig deeper into the eastern and SE states through Friday. Another low pressure trough moving across Southern Canada is expected to push the first low out of the picture, at last, but re-establishment another deep upper level trough near the same location by Friday as the first one which finally also press east through the weekend.
During this course of events, Florida has lost its deep tropical moisture connection (air mass), so most moisture for storms will rely on the ever critical location of surface/mid level boundaries where winds converge to enhance localized deeper moisture such as along Lake/Sea Breezes and mid-level troughs. This could be an ongoing theme through Friday, with the rain chances diminishing to near zero for north Florida (mainly the panhandle region) on Thursday.
TODAY: As usual, transitional periods are tricky at best, especially now that we have lost the deep tropical connection and an apparent mid-level trough axis is elongated down the state; in short, we have an entirely new 'ball game' to play.
SW Flow seems to be the consensus along the east side of the state, albeit quite light. However, as of 12:30pm the ECSB has yet to set up, so the RUC/GFS might just have something there with their propositions of a delayed or at least east coast sea breeze until mid-afternoon . The hamartia for forecast busting today will be just exactly where deeper moisture can re-establishment as a result of moisture convergence as opposed to the free flowing moisture of the past few days.
Showers have already formed near Lake Okeechobee, as residual pockets of fog and low clouds continue to burn off elsewhere. The most unstable atmosphere is along the west coast near TPA and north, and this should move inland during the day across most of the north 1/2 of the state. However, this area is also most dry atmospherically speaking. Sea breeze circulations might not set up in full until mid-afternoon, if not later north of Lake Okeechobee. Meanwhile, a jet stream speed max is apparent coming across the Gulf in model guidance and satellite imagery.
THUS, for today more thunder as opposed to rain showers, but all in all should remain fairly isolated, although there could become a time of better rain coverage by early evening over the interior spreading toward the east coast and offshore, especially along and south of SR 46. Thus, today, like all the others could end up cloudy in many locations along the east side by sunset. South Florida as always should kick off soonest, but the strongest storms will wait for possible sea breeze convergence underneath the mid level trough axis where the deepest moisture resides, which would be further north. The coldest air aloft is near I-4 and north, but only by a very small margin. The strongest storms , although more isolated should be near NE Lake County, Seminole, West Volusia, Flagler, and western St. Johns counties..with another stronger storm or two in St Lucie/Marian Counties and maybe Southern Brevard/Vero area. The strongest storms will result from where two or more boundaries meet late in the day..somewhere along the east side of the state or the interior. Greatest coverage of rainfall does not equate to where the strongest storms will be.
WEDNESDAY/FRIDAY: Late Friday or Saturday could be fall's climacteric, if for only a day or two..more so for the northern 1/3 of the state. Expecting that local forecasts will go up and down on rain chances up until that time due to the uncertainty of where boundaries will be found until the final blow, or front, can press south. As of the 2AM GFS, that would occur Friday night, with the front over or near the Florida Straits by Saturday afternoon. Before that time, thunder is possible..and if timed just right per the GFS early today, would be across Central Florida during peak heating on Friday. Thus, some stronger storms (isolated) could occur this day in that location. The front has yet to be forecast to cleanly clear the Florida Keys, so rain chances might actually pick up in that location over the weekend.
With the frontal passage, whenever that might be, the east coast could expect a 'fall like' morning in the temperature department, but with the progressive southern tier of states pattern in place abetted by the southern branch jet stream, it will be short lived as onshore flow ensues within 24 hours after fropa if not sooner (frontal passage).
NEXT WEEK: We could be setting up for an east coast rain event, most likely south of SR 50 and north of Ft Lauderdale by the middle of next week. The most likely area would be Palm Beach County upstream of the onshore flow off the Bahamas, with the Ft. Pierce area coming in a close second as a contender. Other areas south of I-4 might get in on the act in-part. ..put rain chances do pick up again over South Florida at least due to the lagging mid-level frontal boundary.
In the longer term, a much deeper full latitudinal trough of threatening proportions is forecast to develop in the country's mid section toward next weekend as we progress through the first week of October. Not shown yet, but there is a chance that too will cut off neat the Great Lakes, or could be a severe weather maker at various stages of its frontal life cycle stage from the Central Plains toward the Ohio River Valley and portions of the SE states in the great beyond.