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017 FXUS62 KTAE 290117 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 915 PM EDT Sun Sep 28 2014 ...Heavy Rainfall is still possible through Monday... .Update...
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Through 01z, most of the rainfall has been confined to the Florida zones and adjacent coastal waters. The heaviest rains over land have been along the coast of Gulf and Franklin counties and over portions of the southeast Big Bend. These areas based on radar estimates and reporting gauges have received between 1 and 3 inches of rain. Local radars currently show scattered convection generally along and south of a Panama City to Valdosta line. We still believe that as the upper level trough and eventual develop of a surface low along the central Gulf coast moves east there is still the potential for heavy rainfall across the Tri-state region. For this reason, we will keep the Flash Flood Watch in place. PoPs have been trimmed back slightly for the overnight period but are still in the likely to categorical range. .Near Term [Through Tonight]... The 2 pm EDT regional surface analysis showed a rather ill-defined, quasi-stationary front about 25 to 60 NM offshore the central Gulf Coast, with progressively higher pressure to the northeast. Vapor imagery and upper air data showed Precip water values exceeding 1.5 times normal values across much of our forecast area. Numerous showers and thunderstorms have been developing over the Gulf Coastal waters this morning & early afternoon, but so far the development of rain inland has not been that impressive. However, all of the latest NWP guidance is in agreement in increasing the Q-G forcing across our region overnight, with the approach of a 500 mb trough (currently over east TX). Thus we are confident in the eventual development of rain across our entire forecast area. The main forecast question is the amount of rain. Unfortunately the NWP guidance offers quite a range of possibilities- from very little QPF (with the heavy rain remaining just offshore) to areas exceeding 6 inches. The variety of solutions and lack of a single, well-defined forcing mechanism makes it difficult to make a precise rain amount forecast, but at the overall synoptic environment does point to the potential for heavy rain, especially the abnormally high moisture values. We think that portions of our forecast area will get 1 to 2 inches of rain between now and 8 am EDT Monday, but a few spots could get 6 inches. If these heavier amounts occur in a city (or in any low- lying, poor drainage area), flash flooding could occur. .Short Term [Monday Through Tuesday Night]... With plenty of deep layer tropical moisture already in place across the CWA and points westward (widespread PWATs between 2" and 2.3"), and the forcing for lift coming from a slow moving shortwave now over western LA, a fairly widespread heavy rainfall event is still expected across much of the region through Monday. Storm total rainfall amounts are expected to average between 1.5" to 2.5" across much of SE AL and SW and SC GA, with 2.5" to 4" amounts likely across much of the Florida Big Bend and Panhandle before all is said and done. The heaviest amounts are still likely closest to the coast, with parts of Bay, Walton, Gulf, Franklin, and Dixie counties in FL possibly totaling over 4", with isolated 5-7" amounts not out of the question. Also, given the poor organization and slow movement of this low pressure system, there is still a reasonable amount of uncertainty to warrant a continuation of the Flash Flood Watch for the entire CWA through the day on Monday. PoPs on Monday will range from 60 to 80% through the day, with this rainfall event gradually winding down and coming to an end on Monday Night and Tuesday. With plenty of clouds and rain, High temps tomorrow will struggle to climb into the upper 70s to the middle 80s, with more widespread middle to perhaps upper 80s on Tuesday as more insolation is expected. Low temps both Monday and Tuesday nights should range from the lower to middle 60s N, to the upper 60s to around 70 to the S. .Long Term [Wednesday Through Sunday]... After a very wet pattern over much of the near and short term periods, we expect to have a brief break in the unsettled weather later on Tuesday and through Wednesday, as both Sfc and upper level ridging build in for a short time. Thereafter, showers and thunderstorms are expected to return to the fcst in earnest on Thursday and Friday, as the strongest cold front of the season thus far approaches from the NW. This cold front is expected to bring a real taste of fall to the region by Saturday and Sunday, with low temps possibly reaching the lower to middle 50s over the interior on Sunday morning, with much drier air also building in under the NW flow. High temps will still be very close to climo levels, however, generally in the lower to middle 80s on Sat and Sun. Before the frontal passage, above normal temperatures are expected to persist, with the warm and humid air struggling to budge.
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&& .Aviation...
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[through 00Z Tuesday] Trimmed back mention of TSTMS for most periods of the TAF cycle. Otherwise, fairly pessimistic forecast with MVFR/IFR cigs/vsbys along with periods of rain throughout. Some of the rain may be heavy at times possibly lowering vsbys to LIFR levels, especially at ECP and TLH.
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&& .Marine... Once again, winds and seas are running a little bit higher out of the east to southeast than the models have been projecting, due to the combination of a tighter pressure pattern and the numerous showers and thunderstorms which keep developing over the marine area. However, these winds and seas should stay below cautionary levels through the period, while gradually decreasing. By Tuesday night and Wednesday, winds will diminish to between 5 and 10 knots out of the northeast, with seas dropping to around 1 foot. && .Fire Weather... Hazardous fire weather conditions are not expected over the next few days. && .Hydrology... As mentioned above, storm total rainfall amounts are expected to range from 1.5" well to the north in our HSA, to 4" or more well to the south. Depending on exactly where the highest rainfall totals are observed, will determine the potential flooding impacts on our area rivers and streams. At the present time, the rivers most likely to be impacted with significant rises would be the Choctawhatchee, Apalachicola, and the Suwannee, though it would likely take more rainfall than we are currently forecasting to bring them into flood stage. .Preliminary Point Temps/PoPs... Tallahassee 71 86 69 87 67 / 80 70 50 30 10 Panama City 73 85 70 85 72 / 80 80 40 20 10 Dothan 69 83 64 87 64 / 80 80 30 10 10 Albany 70 81 65 86 64 / 80 80 30 10 10 Valdosta 71 83 67 85 63 / 80 80 50 30 10 Cross City 71 85 70 86 66 / 80 70 60 40 10 Apalachicola 74 85 72 83 72 / 80 70 50 30 10 && .TAE Watches/Warnings/Advisories... FL...Flash Flood Watch through Monday evening for Calhoun-Central Walton-Coastal Bay-Coastal Dixie-Coastal Franklin-Coastal Gulf-Coastal Jefferson-Coastal Taylor-Coastal Wakulla- Gadsden-Holmes-Inland Bay-Inland Dixie-Inland Franklin- Inland Gulf-Inland Jefferson-Inland Taylor-Inland Wakulla- Inland Walton-Jackson-Lafayette-Leon-Liberty-Madison-South Walton-Washington. High Rip Current Risk until 6 PM EDT this evening for Coastal Franklin. GA...Flash Flood Watch through Monday evening for Baker-Ben Hill- Berrien-Brooks-Calhoun-Clay-Colquitt-Cook-Decatur-Dougherty- Early-Grady-Irwin-Lanier-Lee-Lowndes-Miller-Mitchell- Quitman-Randolph-Seminole-Terrell-Thomas-Tift-Turner-Worth. AL...Flash Flood Watch through Monday evening for Coffee-Dale-Geneva- Henry-Houston. GM...None. && $$ UPDATE...BARRY NEAR TERM...FOURNIER SHORT TERM...GOULD LONG TERM...GOULD AVIATION...BARRY MARINE...GOULD FIRE WEATHER...BARRY HYDROLOGY...GOULD/FOURNIER

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