Area Forecast Discussion
Issued by NWS Jacksonville, FL
Issued by NWS Jacksonville, FL
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645 FXUS62 KJAX 240811 AFDJAX Area Forecast Discussion National Weather Service Jacksonville FL 411 AM EDT Tue Sep 24 2024 ...TROPICAL STORM IMPACTS BEGINNING AS EARLY AS LATE WEDNESDAY NIGHT... ...MINOR TIDAL FLOODING CONTINUES WITH ST JOHNS RIVER... .NEAR TERM... Clear skies and near calm winds early this morning will see the potential for some fog to development along inland locations during the predawn hours. Any fog that does develop should begin to clear a hour or so after sunrise. Otherwise, another day of mostly dry conditions as the ridge of high pressure from the past few days begins to shift off towards the western Atlantic as the day progresses. Daytime Highs expected in the low 90s along inland locations with coastal locations in the upper 80s as onshore winds will keep temperatures a bit cooler. Overnight into Wednesday, temperature lows will primarily be in the low 70s with coastal locations a bit warmer in the mid 70s. ~~ MESSAGE OF THE DAY ~~ With another day of quiet weather, review plans and ensure necessary supplies are assembled in the event of tropical storm or hurricane impacts later on this week. Please pay close attention to the forecast information locally as well as from the National Hurricane Center to stay abreast of the latest forecast information. For the latest NE FL and SE GA Daily Key Messages please visit: https://www.weather.gov/media/jax/briefings/nws-jax-briefing.pdf && .SHORT TERM...(Wednesday through Friday)... A tropical system (currently Potential Tropical Cyclone Nine, but forecast to become Hurricane Helene) will begin to accelerate north- northeastward in the eastern Gulf of Mexico through Wednesday and is forecast to rapidly intensify into a Major Hurricane prior to landfall somewhere along the eastern Panhandle and Big Bend region of Florida Thursday. This will be a broad system and impacts will extend well away from the cyclone`s center with impacts beginning locally across Northeast Florida as early as late Wednesday night and linger through early Friday. Ahead of the main window of impacts, coastal conditions will become breezy through Wednesday as gradients begin to tighten between PTC-9 and a surface high situated to the north. There may be some convergent bands of showers amid the southeasterly flow ahead of the actual rainbands spiraling from the accelerating tropical system. Increasing chances are expected early Thursday as rain bands begin to push northward across the area. If timing hold, which is not a certainty given the speed the system is predicted to gain, the early hours Thursday may be a period of concern regarding isolated tornadoes. Additional concerns will be the potential for tropical storm force winds, flooding rainfall, and at least moderate tidal flooding Thursday and into Friday. Despite the relatively fast movement of system, a footprint of 3 to 6 inches of rainfall along the I-75 corridor in NE FL, Suwannee Valley and interior counties of SE GA is predicted. Undoubtedly, there will be locally if not scattered areas where amounts are higher. Given the moderate confidence in excessive rainfall, elected to hoist a Flash Flood Watch for those aforementioned areas (this may be expanded eastward with any shifts in the track to the east). By Thursday night and through Friday the tropical cyclone will be pulled to the north and begin to phase with the baroclinic, stacked low centered to the northwest. The so-called "tail" may linger across NE FL Friday continuing chances for showers which may train the area through the afternoon. Power outages and lack of adequate cooling on Friday may lead to heat impacts as temperatures rise into the upper 80s and low 90s and heat index pushing into the lower 100s. && .LONG TERM...(Friday night through next Tuesday)... What`s left of Potential Tropical Cyclone Nine (PTC-9; likely to become Tropical Storm Helene) will pull away to the north as it phases with the near stationary low pressure system along the mid Mississippi River valley. As it does so, a trailing front will push south of the area briefly before lifting back to the north and stalling across northeast Florida through at least early next week. Southwesterly flow between the broad cutoff upper low to the northeast and upper ridge east of the Bahamas will steer shortwave impulses along the aforementioned stationary boundary, triggering waves of showers and scattered thunderstorms each day. Though there isn`t a significant amount of cumulative rain forecast (1-3") with those passing impulses, there may be flood concerns given the heavy dose of rainfall expected with PTC9 on Thursday, creating more sensitive conditions this weekend and early next week. Temperatures will trend down initially and are expected to hover in the 80s for high temperatures due to prevailing cloudiness and waves of rainfall. && .AVIATION... (06Z TAFS) Issued at 115 AM EDT Tue Sep 24 2024 Light variable winds with VFR conditions for the next few hours for coastal sites. Inland areas will begin to see formation of patchy fog during the predawn hours and clearing by 13Z. East- southeasterly winds will redevelop by 15Z with speeds from 5-10 kts. Winds will again begin to wane by 00Z on Wednesday night. && .MARINE... The lingering high pressure will shift off towards the east through today. Southeasterly winds will begin to increase through the day getting into the 10-15 kt range by this evening. Come Wednesday, Small Craft Advisory conditions is expected to develop during the evening hours. As Potential Tropical Cyclone 9 heads into the gulf on Wed morning, winds will continue to strengthen with tropical storm conditions possible by early Thursday and continue into Thursday night. There is still uncertainty in the scale, intensity, and track of the tropical system as it develops. All of those factors will influence the local coastal water conditions. Some gradual improvement on Friday as the system pulls away to the north. A trough may linger over the region Friday night into the weekend with winds and seas below small craft advisory levels. Rip Currents: Moderate risk of rip currents this afternoon for area beaches. High risk of rip currents on for all area beaches by Wednesday as southeast flow increases as the approach of the tropical system from the Gulf brings impacts to the local area waters. && .HYDROLOGY... Action to minor tidal flooding continues within the St Johns River basin through mid week before influences from potential tropical cyclone 9 tracking northward across the eastern Gulf of Mexico begin. Strong southeasterly flow in response to the tropical system may bring tidal levels back into Minor or low-end Moderate flood at times of high tide along the Atlantic coast by Thursday evening. Given the current elevated tides already ongoing in the St Johns River, the potential for Moderate Flooding and impacts are possible during at least Thursday and Friday high tides. With the potential for increase rainfall from the potential tropical cyclone, A Flash Flood Watch from Wednesday evening through Friday morning for locations to the western counties of the CWA. Preparations should be considered for low-lying areas along the St Johns River, especially in the Downtown Jacksonville, San Marco, & Riverside areas along with other flood prone locations in the upper St Johns in Clay, St Johns, and Putnam counties. && .PRELIMINARY POINT TEMPS/POPS... AMG 91 69 88 72 / 0 0 20 50 SSI 86 76 85 76 / 0 0 10 50 JAX 90 74 88 76 / 0 0 30 60 SGJ 88 76 88 76 / 0 0 30 70 GNV 91 71 89 74 / 0 0 40 70 OCF 93 73 90 76 / 0 0 50 70 && .JAX WATCHES/WARNINGS/ADVISORIES... FL...Flood Watch from Wednesday evening through Friday morning for FLZ021-035-120-136-220-236-240-322-340-422-522. Coastal Flood Advisory until 5 PM EDT Wednesday for FLZ033-038- 125-132-137-225-325. GA...Flood Watch from Wednesday evening through Friday morning for GAZ132-133-149-162-163. AM...None. && $$