"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, September 23, 2010

First Full Fall Day Ushers In Somewhat Frenetic Florida Forecasts

Image: A Harvest Moon occurred nearly coincident with the start of fall at 11:09pm last night. The next time these two events will be so closely tied together will be in 2029.
SYNOPSIS: Broad expanse of high pressure extends across the Atlantic Ocean into the S.E. U.S. Low pressure across the Caribbean, Yucatan Peninsula, and into the SW Gulf is flayed out south of the high pressure creating a deep, easterly flow component to the wind field.
Invest 95L  within this area of low pressure in the South-Central Caribbean, well south of the Dominican Republic, is becoming organized as it moves generally west. This area is part of a tropical wave that was generated from an African off shoot, the other part of which became Julia; that storm remains loitering well off in the Eastern Atlantic. Atmospheric moisture over Central and South Florida on the increase producing sporadic rain showers, most concentrated over the Keys at time of writing. Other widely dispersed showers making it to land from Daytona to Miami. This moisture field is working north today. Elsewhere, a trough is passing across Minnesota this morning generating a flood/severe storm threat over the upper Mid-West region this morning and this afternoon. This area will move east and be replaced by a second one as we head into late Friday. Believe it or not, it is the second one that will be the indicative harbinger of things to come way down here in Florida as we head into the beginning of next week! So watch the weather in Minnesota, because what hits there will eventually be affecting this state indirectly in the days to come. Also, I haven't heard mention of this anywhere, but there is a weak upper level low over the central  Gulf of Mexico that I first noted late yesterday which is evident on satellite imagery. The NAM model did not pick up on this feature very well, but the GFS nailed it on the 300-200mb analyses. This is a seemingly insignificant feature in the short term, but in the long term could contribute to the long term eventualities of what will occur as the second Minnesota short wave digs southward through the weekend. Just thought I'd throw that out there for good measure.
TODAY-TONIGHT: Nothing new as far as temperatures or winds at the surface and aloft. They are all generally from the east. The only change is the gradual increase of PWAT (precipitable water) values. As such, the chance of rain showers passing overhead today over Central Florida will increase just a bit, but more so from Vero Beach and points south, especially by later this afternoon. The depth of moisture isn't overly tremendous, but low level availability of what is there is enough to generate showers as far north as Ormond Beach, just more so the further south one goes as amount and depth within the atmosphere increases. As such, best chances of rain today south of Vero Beach at almost anytime...with detectable chances further north with time, especially late. Probably not much in the thunder category due to warm air aloft, although some could occur over the far interior and western portions of South-South Central Florida late in the afternoon.
FRIDAY: By sunrise, PWAT values over Central Florida will have climbed to levels we have not seen for quite some time now from near New Smyrna Beach south. The moisture will have already been in place from Jupiter Inlet and south for a good 12 hour previous. Moisture levels will sustain themselves throughout the day, with perhaps a greater depth to the moisture field from Jupiter Inlet - Ormond Beach and west across the state by late in the day and into Saturday. As such, rain chances tomorrow will be higher for Central Florida than for today, but thunder not anticipated. Not an all day rain event by any means. Just more clouds in the low and mid levels, with more showers coming in off the Atlantic. Easterly flow will prevail, but begin to weaken over night Friday into Saturday. Showers on Friday could occur any time day or night. Just look toward the east from whilst they will arrive.
SATURDAY-SUNDAY: Already stepping into 'dangerous forecast territory' from Saturday and beyond, so will go with the broad brush for South and Central Florida. It looks as though the deepest moisture will be over Central Florida rather than further south over the weekend. Both the GFS and NAM are highlighting the highest concentration or likelihood of showers, some heavy, from Sebastian Inlet to Daytona Beach along the immediate east coast (very generally east of I-4). The GFS kicks it up a notch with a vorticity max riding up the Florida East Coast over night Friday and lingering just offshore through all of Saturday and into Sunday. Would expect considerable cloudiness on Saturday as a result with continued east winds, but less in strength than what we've been seeing the past week. The potential for some of this activity to active lightning will increase as we work into the latter portion of the weekend, but can't discount 'ocean thunder' on Saturday.  Rain chances should be highest on Saturday as will rainfall totals as storm motion should slow considerably. Mid-Upper level winds to wane as a break in the overall synoptic scale pattern which has been in place for a few weeks finally breaks down. That second system alluded to near Minnesota begins to drop south along the Mississippi River Valley toward the Deep South and ridge axis makes the break, placing all of Florida in weak pressure fields, nearly a COL in fact. And one that is filled with moisture at that.
MONDAY-BEYOND: Chance of having thunderstorms over South and Central Florida increases as moisture laden steering changes from what was easterly becomes nearly calm to now S-SW. Temperatures remain status quo with lows in the mid 70s inland to nearly 80 east of US1. Perhaps a few degrees cooler than days of recent due to weakening of the easterly gradient flow, hence less advection of warm ocean water temperatures during the over night. Highs in the upper 80s to very low 90s. As such, the coast could see upper 70s for a change across the boards which would be a pleasant change. Now, the BEYOND portion will be briefly discussed in the TROPICS portion, since that is what the 'future' will be all about for the entire state next week.
TROPICS: As noted, we have Invest 95L in the South Central Caribbean. A lot of emphasis has been placed (from what I've heard and read) on this system becoming the next depression or storm. Upon review of the forecast tropical model plots, as well as the GFDL, GFS, ECMWF, HWRF, and NOGAPS models, there is a very close consensus as to what will occur in the near term period. That being, the system heads toward the Yucatan. It's what happens from there that things diverge. I'm intrigued by implications made by the GFS, namely because it takes the what will by that time be '95L turned depression or Storm Matthew into the Yucatan while yet another Invest develops near Jamaica in its wake. It is this second area the model eventually develops into what could be of immediate interest as far as Floridians are concerned as it is the second one that would be either Matthew or maybe even Nicole (if 95L/Depression gets named).
On the other hand, the majority of the other models leave what would be solely Matthew just east of the Yucatan or partially over it and begin to deviate it northward with time. As you can see, we are well into Science Fiction at this point in time. So point is, we'll be reading/hearing/seeing lots of fiction on the press until things become a reality.
As long as we are talking fiction, and since I mentioned the GFS evolution of things to come already, we can take it a step further. The GFS way out out there takes this 'second yet to be system' across Florida as what appears would be a depression accompanied by copious rainfall, into roughly Eastern Georgia and merges it with what would be that what would be the system out of Minnesota. Talk about irony. But it doesn't end there. It's the NEXT system after that, as we end the first week of October...that could be the big player for somewhere in the Gulf Coast.
Point being in mentioning this, is  illustration that although as one would expect at this time of year, this is all completely ambiguous, the trend is indicative that a somewhat prolonged period of unsettled tropically associated weather over the state of Florida to varying degrees, could be well at hand September 25th - October 9th (more tropical at times than others). The good thing for east coasters though, as things look now none of these yet to develop systems would pose a Storm Surge threat to the east coast.

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