Area Forecast Discussion
Issued by NWS Jacksonville, FL
Issued by NWS Jacksonville, FL
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778 FXUS62 KJAX 260754 AFDJAX Area Forecast Discussion National Weather Service Jacksonville FL 354 AM EDT Thu Sep 26 2024 ...HURRICANE HELENE WILL MAKE LANDFALL THIS EVENING OVER THE BIG BEND REGION ON FLORIDA... ...MINOR TIDAL FLOODING CONTINUES WITH ST JOHNS RIVER... ...New NEAR TERM, SHORT TERM, LONG TERM, MARINE, HYDROLOGY... ...New NEAR TERM, SHORT TERM, LONG TERM, MARINE... .NEAR TERM... Issued at 354 AM EDT Thu Sep 26 2024 For the latest NE FL and SE GA Daily Key Messages please visit: https://www.weather.gov/media/jax/briefings/nws-jax-briefing.pdf Hurricane Helene will continue to move north across the Gulf of Mexico today, making landfall sometime late this evening along the Big Bend of Florida. Outer rain bands from Helene will move through northeast Florida and southeast Georgia, bringing showers and storms for most locations. Within any showers and storms, there will be the potential for isolated tornadoes to develop over inland locations with the rain bands. As low-level shear increases and the large wind field of Helene spans across the Florida peninsula, the highest potential for tornado development will be along coastal Duval and northward along coastal locations of southeast Georgia, with potential waterspouts possibly making their way onshore with the southeasterly flow. General timing for the increase potential for tornado development will be from 5pm to 11p. Highest winds away from the center of the system are expected to occur along coastal sites, with gusts up to tropical storm speeds (~65mph), with the Suwannee Valley region possibly getting sustained winds up to Hurricane force speeds as Helene nears and makes landfall. With the elevated southeasterly flow, this will lead to the potential for waters from the upper St. Johns to be pushed northward into the lower St. Johns which can lead to flooding along the low-lying areas along the St. Johns river, particularly downtown Jacksonville. In addition to the wind threat, localized flooding for those locations which may still have saturated soils as the past month has been one of the wettest with record rainfall amounts. While rainfall totals have trended down from earlier estimates, additional periods of heavy rainfall will still be a factor for those locations with saturated soils as well as low-lying poor drainage areas. && .SHORT TERM... (Friday through Saturday night) Issued at 354 AM EDT Thu Sep 26 2024 Helene will continue to zip northward through the day Friday, gradually transitioning to an extratropical system while merging with an upper low near the Ohio River Valley. A dry slot aloft to the south and southwest of the departing system works its way in for Friday, which will generally limit rain chances for most of the area as a developing frontal boundary sits just south of the region. The best chance for any showers and perhaps some isolated thunder will be south of about Gainesville to Saint Augustine, and especially during the first half of Friday. The southwesterly flow within the dry slot will be pretty breezy, with winds in the 15-20mph range and gusts up to 25-35mph. This flow direction should also allow temps to climb to the upper 80s to near 90 near the I-95 corridor and to the coast, with low to mid 80s over the interior. The same upper low essentially sits and spins almost in place near the western Ohio River Valley Friday Night and through Saturday, which should keep the southwesterly flow and some drier air into the area through this time frame. There is some discrepancy remaining with respect to where the exact moisture/frontal boundary sets up and therefore extent of convection. However, expecting at least slightly higher rain chances for parts of the area Saturday, with again the best chances being south and west of I-10 and south of Gainesville to Saint Augustine as with Friday. Winds will settle down a bit compared to Friday, though still in the 10-15mph range with gusts in the 20s. Temperatures will be similar to Friday, upper 80s to near 90 south and east and mid 80s north and west. && .LONG TERM... (Sunday through Wednesday) Issued at 354 AM EDT Thu Sep 26 2024 The remnant mid/upper low starts to broaden and elongate by the end of the weekend and into the start of next week, eventually drifting offshore the eastern seaboard around the Tuesday to Wednesday time frame as a weakening trough. Similar to the start of the weekend, certainly still some discrepancy with long range guidance regarding extent of available layer moisture and the position of a nearly stalled front. Given the overall wet pattern of recent and lingering dynamics with the upper low/trough, leaning towards chances of showers and storms continuing for generally the southern half of the CWA for at least the start of next week, possibly dropping lower by mid week if a more subsident airmass builds in north and west of the departing upper feature. Temperatures for this period start generally slightly above normal, though trend closer to normal towards midweek. && .AVIATION... (06Z TAFS) Issued at 213 AM EDT Thu Sep 26 2024 Lingering TS around SSI through the next couple of hours, as light showers and some TS expected for the other TAF sites through the rest of the overnight hours as outer rain bands from Helene move northward. Heavier rainfall expected by 12Z - 13Z with some TS as more rainbands move through. Wind gusts from 35kt to 40kt possible through the rest of the TAF period as Helene nears landfall near 00Z to 06Z. && .MARINE... Issued at 354 AM EDT Thu Sep 26 2024 Hurricane Helene continues to move northward through the gulf early this morning. Southeasterly winds will gradually strengthen through the day reaching tropical storm strength by the morning hours, lingering at these levels into Friday. The tropical system will begin to move away from the area sometime on Friday. With a trough lingering over the area into the weekend, conditions are not expected to be at small craft advisory levels. Rip Currents: High risk of rip currents on for all area beaches through Friday as southeasterly flow increases ahead of Hurricane Helene over the Gulf of Mexico. && .HYDROLOGY... Issued at 354 AM EDT Thu Sep 26 2024 A Flood Watch for all of southeast Georgia and northeast Florida is in effect. Excessive rainfall due to Hurricane Helene will likely result in scattered areas of flash flooding and isolated episodes of considerable flash flooding, particularly in urban flood prone locations and areas that received a lot of rainfall this month. Widespread 3-6" of rain is forecast, with locally higher amounts. 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. && .PRELIMINARY POINT TEMPS/POPS... AMG 80 73 85 67 / 90 80 10 0 SSI 83 78 88 73 / 80 80 10 10 JAX 85 77 90 73 / 90 80 20 10 SGJ 86 78 91 75 / 90 80 20 10 GNV 85 75 88 72 / 80 70 20 10 OCF 86 77 90 74 / 90 70 20 10 && .JAX WATCHES/WARNINGS/ADVISORIES... FL...Tropical Storm Warning for FLZ023-024-030-031-033-038-124-125- 132-133-136>138-140-225-232-237-240-325-425. Flood Watch through Friday morning for FLZ021-023-024-030-031- 033-035-038-120-124-125-132-133-136>138-140-220-225-232-236- 237-240-322-325-340-422-425-522. Hurricane Warning for FLZ021-035-120-220-236-322-340-422-522. Coastal Flood Advisory until 8 AM EDT Friday for FLZ033-038-132- 137. Coastal Flood Warning until 8 AM EDT Friday for FLZ124-125-133- 138-225-325. High Rip Current Risk through Friday evening for FLZ124-125-133- 138. High Surf Advisory until 4 PM EDT Friday for FLZ124-125-133-138. GA...Tropical Storm Warning for GAZ133>136-151>154-165-166-250-264- 350-364. Flood Watch through Friday morning for GAZ132>136-149-151>154- 162-163-165-166-250-264-350-364. Hurricane Warning for GAZ132-149-162-163. Coastal Flood Warning until 8 AM EDT Friday for GAZ154-166. High Rip Current Risk through Friday evening for GAZ154-166. High Surf Advisory until 4 PM EDT Friday for GAZ154-166. AM...Tropical Storm Warning for AMZ450-452-454-470-472-474. && $$