Area Forecast Discussion
Issued by NWS
Issued by NWS
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114 FXUS62 KTAE 251552 AFDTAE Area Forecast Discussion National Weather Service Tallahassee FL 1152 AM EDT Wed Sep 25 2024 ...FLOOD WATCH IS NOW IN EFFECT THROUGH FRIDAY MORNING... ...New UPDATE... .UPDATE... Issued at 1149 AM EDT Wed Sep 25 2024 Minimal changes to the temps and PoPs this morning as the forecast looks to remain on track today. A Flood Flood watch is now in effect through Friday morning for the entire area. && .NEAR TERM... (Today and tonight) Issued at 501 AM EDT Wed Sep 25 2024 Somewhat unrelated to Helene, showers and thunderstorms will blossom over the service area today, particularly west of a line from Tallahassee to Albany. 1000-700 mb layer flow will become more southerly this morning, mostly due to the upper trough axis that will move from the Ozarks to the Lower Mississippi Valley today. Precipitable Water (PW) values will steadily tick up above the very moist 2-inch mark. The rich moisture and pockets of moderate instabililty will interact with a surface boundary over the Panhandle and Lower Alabama, along with a nearshore landbreeze boundary, to bring a significant blossoming of showers and thunderstorms for the rest of this morning. With the surface boundary being a slow-mover, we could see training or backbuilding that could lead to localized flooding issues. 25-35 knots of effective bulk shear could organize storms into clusters containing gusty winds and the outside chance of a brief tornado. By tonight, we will more squarely come under the right entrance region of a jet streak to our north. This favors upper level divergence and large-scale lift. Stratiform rain with embedded thunder will expand tonight, way out in advance of Helene. && .SHORT TERM... (Thursday through Thursday Night) Issued at 501 AM EDT Wed Sep 25 2024 Helene is expected to make landfall as a major hurricane along the Big Bend coast late Thursday. The center of Helene will quickly move north through our Georgia counties on Thursday night. Helene is forecast to be a Category 3 on the Saffir-Simpson Hurricane Wind Scale at landfall, qualifying as a major hurricane. Guidance has been tightly clustered on the track through the Big Bend region, and the official hurricane forecast track has changed very little over the last 24 hours. See the latest NHC discussion for storm-centric forecast rationale on Helene. Helene will be a spatially large hurricane. The wind radii forecast shows tropical-storm force winds (39+ mph sustained winds) extending 250 miles east of the center, and about 120 miles west of the center at landfall. Its fast forward speed and large circulation will support damaging winds spreading well inland through our Georgia counties on Thursday night, especially counties near the I-75 corridor. The 5 am NHC advisory carries a swath of hurricane-force winds all the way north through our Georgia counties, i.e. to north of the U.S. Hwy 82 corridor. Despite the fast forward motion of Helene, its size along with additional lift from mid-latitude jet dynamics will support heavy, flooding rain. As the northwest part of Helene`s circulation interacts with a stalled front to its northwest, a stripe of heavy 6- 10 inch rains could develop left of the center track. Considerable flash flooding is possible, especially coming on the heels of todays unrelated heavy rain. Tropical-cyclone tornadoes will mainly be a concern in rain bands to the east of the center, with the greatest concern over our Suwannee Valley and I-75 corridor counties. There has been no change to the storm surge forecast with the 5 am advisory. Despite the fact that some storm surge guidance increased overnight, the previous forecast was already intended to cover a reasonable worst case scenario, so it therefore still covers the situation well. Given the onset timing of tropical-storm force winds, Hurricane Watches in our far south Georgia counties are now being upgraded to Hurricane Warnings, while expanding those warnings north past the U.S. Highway 82 corridor to fit the latest NHC forecast. Today is the day to complete your outdoor preparations for Helene. Winds will increase quickly at some point during the day on Thursday, but the large area of rain and embedded thunder on Thursday morning could make it inconvenient to be outdoors by then. && .LONG TERM... (Friday through Tuesday) Issued at 501 AM EDT Wed Sep 25 2024 TC Helene is progged to be north of our CWA at the beginning of this long term period. Morning showers and perhaps an isolated thunderstorm will quickly move out of the area as southwesterly winds advect drier air behind the departing Helene. As it reaches the Ohio Valley, it will be absorbed by an upper low in the Midwest overnight Friday night. Conditions will be generally dry later Friday morning through Saturday with highs in the mid to upper 80s for any immediate cleanup and recovery operations. That upper low drifts eastward and off the east coast Tuesday. Rain chances associated with this feature, as well as a weak frontal boundary closeby, will be low (20-30%) Sunday through Tuesday ahead of northwest flow behind the departing trough and another round of dry air working in mid week. High temperatures Sunday through Tuesday will continue to feature highs in the mid to upper 80s and lows in the upper 60s to lower 70s. && .AVIATION... (12Z TAFS) Issued at 648 AM EDT Wed Sep 25 2024 Southerly flow aloft will bring a more richly moist and moderately unstable air mass north off the Gulf. This will interact with a surface boundary over the Panhandle and southeast Alabama, along with a landbreeze near the Panhandle coast, to bring a blossoming of convection over ECP this morning, expanding north to DHN. TLH and ABY will be near the eastern edge of convection through the morning. This afternoon, rain-cooled air near ECP and DHN may bring a decrease in convection, but areas to the east that did not previously see thunder will warm up and see convection bubbling up in the afternoon. A large area of stratiform rain and embedded thunder will spread north this evening, well in advance of Helene. This will bring a more widespread reduction in cigs and visibilities, lowering through the night. && .MARINE... Issued at 501 AM EDT Wed Sep 25 2024 At 5 am EDT Wednesday, the center of Tropical Storm Helene was located over the far northwest Caribbean Sea. Helene will move northward across the eastern Gulf later today and Thursday, rapidly intensifying to a major hurricane before making landfall along the Big Bend Coast late Thursday. Helene will quickly move inland on Friday, so conditions will improve over the waters. Gentle to moderate southwest breezes will prevail this weekend, as a large area of low pressure spins over the Lower Mississippi Valley. && .FIRE WEATHER... Issued at 501 AM EDT Wed Sep 25 2024 Helene is expected to make landfall as a major hurricane along the Big Bend coast late Thursday. Heavy, flooding rain will begin as soon as tonight, well in advance of the center of Helene. Tree damage will be most widespread in the right eyewall of the hurricane. The fast forward speed of the hurricane will spread damaging winds further inland than your typical hurricane, posing the risk of tree damage well north into our Georgia districts. Preparations for Helene should be completed today. Weather conditions will improve rapidly early Friday, and sunshine will return. && .HYDROLOGY... Issued at 501 AM EDT Wed Sep 25 2024 Primary focus continues to be on the approach of Tropical Storm Helene to the region. The system has the potential to bring significant rain to the region, even accounting for its fast forward motion as it nears the Florida Big Bend. Model guidance has been in good agreement that a precursor event of heavy rainfall will overspread the Florida Big Bend and Panhandle today and tonight with the bulk of the rainfall arriving later on Thursday. A slight risk for flash flooding (level 2 out of 4) through tonight exists in the western Florida Big Bend with a marginal risk (level 1 of 4) in all other areas of the CWA. The entire forecast area is included in a Moderate risk for flash flooding (level 3 out of 4) for Thursday. It is possible that this risk level is increased in future outlooks. Rainfall amounts across North Florida and South Georgia totaling 5 to 10 inches of rain with isolated maximum totals approaching 10 to 15 inches are forecast through early Friday. These amounts will lead to considerable urban flash flooding along with the potential for moderate flooding, especially on the Ochlockonee River Basin. Depending on where the heaviest rains are distributed inland, it is entirely possible that other river basins could experience moderate riverine flooding in the days ahead. For storm surge information, please refer to the latest information from the National Hurricane Center. This is an extremely dangerous storm surge threat in the Apalachee Bay. Storm Surge around Apalachee Bay will not just merely be a coastal event in this system, but will spread many miles inland. If ordered to evacuate, heed the advice of local emergency managers - it could save your life! && .SPOTTER INFORMATION STATEMENT... Spotter activation is not requested. However, spotters are always encouraged to safely report significant weather conditions when they occur by calling the office or tweeting us @NWSTallahassee. && .PRELIMINARY POINT TEMPS/POPS... Tallahassee 86 72 79 71 / 70 90 100 80 Panama City 85 72 79 72 / 80 90 100 60 Dothan 83 70 76 67 / 90 80 100 80 Albany 87 71 78 70 / 70 90 100 90 Valdosta 88 72 82 72 / 70 80 100 80 Cross City 90 73 86 76 / 80 90 100 70 Apalachicola 84 73 80 74 / 80 90 100 60 && .TAE WATCHES/WARNINGS/ADVISORIES... FL...Flood Watch through Friday morning for FLZ007>019-026>029-034- 108-112-114-115-118-127-128-134. Tropical Storm Warning for FLZ007>010-012-108-112. Hurricane Warning for FLZ011-013>019-026>029-034-114-115-118-127- 128-134. Storm Surge Warning for FLZ027-115-118-127-128-134. High Rip Current Risk through late Friday night for FLZ114-115. Storm Surge Watch for FLZ114. GA...Flood Watch through Friday morning for GAZ120>131-142>148- 155>161. Hurricane Warning for GAZ120>131-142>148-155>161. AL...Flood Watch through Friday morning for ALZ065>069. Tropical Storm Warning for ALZ065>069. GM...Tropical Storm Warning for GMZ750-770. Hurricane Warning for GMZ730-752-755-765-772-775. && $$ NEAR TERM...Haner SHORT TERM...Haner LONG TERM....Scholl AVIATION...Haner MARINE...Haner FIRE WEATHER...Haner HYDROLOGY...Godsey