Flash Flood Guidance
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Issued by NWS
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286 AWUS01 KWNH 262308 FFGMPD FLZ000-GAZ000-ALZ000-270500- Mesoscale Precipitation Discussion 1070 NWS Weather Prediction Center College Park MD 707 PM EDT Thu Sep 26 2024 Areas affected...Florida Big Bend well up into Georgia Concerning...Heavy rainfall...Flash flooding likely Valid 262305Z - 270500Z Summary...Hurricane Helene will make landfall late this evening along the Florida Big Bend with inner bands progressing up Georgia and converging on a stationary front over eastern AL. The eyewall will impact the Big Bend area 02 to 05Z which will include heavy rainfall that will exacerbate the extreme impacts from wind and storm surge there. Discussion... GOES-E IR imagery and regional NEXRAD here at 23Z depict a well defined eye on Helene with a central dense overcast extending into Apalachee Bay. Outer bands extend north through the Atlanta metro with a sharp cutoff on the west side on the stationary front that is just into AL. Extreme moisture advection persists ahead of Helene on ever strengthening cyclonic flow with 2.5"+ PW in the inner core of the storm. This exceptionally moist air continues to pivot northward into an area of intense deep layer ascent driven via strong mid-level divergence overlapping the diffluent right entrance portion of a northward arcing jet streak over northern AL. Continuous rainfall with rates around 1"/hr will persist ahead of Helene with embedded areas of 2"/hr in the heaviest bands through midnight. Training of these rates will result in widespread additional rainfall of 2-3" by midnight. A corridor of 3 to 6" along and west of the eyewall, which includes Tallahassee, is forecast through 05Z by the 20Z HRRR which seems reasonable given the increasing forward speed of the hurricane. The area southwest of Tallahassee which has seen 6-10" over the past 24hrs is progged to be just west this eyewall maxima through 04Z. Expect flooding concerns to continue in the Atlanta metro this evening with the additional couple inches. However, the greater threat for Atlanta is early Friday morning as the remnant eye passes to the east. Further details on rainfall from that will come from overnight products. Jackson ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...BMX...FFC...JAX...TAE...TBW... ATTN...RFC...SERFC...NWC... LAT...LON 34218470 33868416 32948314 31568276 30448259 29618275 29158322 29818392 29518483 29658539 30228586 30348596 31698596 32868571