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KEY MESSAGES

For the latest NE FL and SE GA Daily Key Messages please visit: https:/www.weather.gov/media/jax/briefings/nws-jax-briefing.pdf

- Strong Thunderstorms Over Portions of Southeast GA this Evening. Brief Wind Gusts of 40-50 mph, Frequent Lightning Strikes, and Torrential Downpours are Possible within Stronger Storms.

- Widely Scattered Afternoon and Evening Thunderstorms from Tuesday through Sunday. Strong Storms Are Possible Across Portions of Southeast GA on Tuesday Afternoon and Evening.

- Heat and Humidity Builds this Week through the Weekend. Heat Advisories Possible Each Afternoon and Evening from Tuesday through Sunday.

UPDATE

Evening surface analysis depicts high pressure (1021 millibars) centered near the FL Big Bend region. Aloft...deep-layered ridging was positioned over central FL. Latest GOES-East derived Total Precipitable Water imagery indicates that tropical moisture remains in place, with PWATs near or above 2 inches persisting across much of our area. Unstable westerly flow to the north of the deep-layered ridge axis continues to steer weak shortwave energy eastward across the Deep South, with convective outflows from activity earlier this evening over the Okefenokee Swamp and coastal southeast GA merging to keep generating thunderstorms along the U.S. Highway 301 corridor in southeast GA. Strong storms that had been nearly stationary near the Altamaha River entrance slipped southeastward across Little St. Simons Island this evening, with this activity now pushing over the Atlantic coastal waters adjacent to southeast GA. Convection along the U.S.-301 corridor in southeast GA should dissipate before midnight, with debris cloud cover thinning out over our area during the overnight and predawn hours. Lows tonight will only fall to the mid and upper 70s at most locations, ranging to around 80 at coastal locations.

We have increased coverage of showers and thunderstorms on Tuesday afternoon and evening along the I-95 and U.S.-301 corridors from Duval County northward, as deep-layered ridging continues to retrograde and another shortwave trough embedded within the developing west-northwesterly flow pattern aloft glides across our region during the afternoon and evening hours. Strong storms will be possible with this southeastward moving convection during the mid to late afternoon hours, with activity possibly crossing the FL/GA border during the late afternoon or early evening hours before moving offshore. Isolated to widely scattered convection will be possible elsewhere tomorrow afternoon and evening, mainly along mesoscale boundaries such as the Atlantic and Gulf sea breezes. The prevailing westerly flow pattern will boost highs to mid and upper 90s inland, with a later developing and likely pinned Atlantic sea breeze allowing coastal highs to soar to the low and mid 90s. Heat Index values will likely peak in the 105-110 degree range at most locations, and Heat Advisory may be required for portions of our area on Tuesday afternoon and evening.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Main Highlights This Period:

- Daily Isolated to Scattered Afternoon Thunderstorms, some of which could be strong.

- Increasing Heat Index Values near Heat Advisory levels each day. Convective developments are expected to be more inhibited for northeast Florida on Tuesday as high pressure moves across central Florida from out of the east and drier air associated with a northwesterly flow passes over the forecast area. Scattered showers and storms will become relatively more widespread by Wednesday as high pressure moves more into the Gulf and higher levels of moisture cross over portions of southeast Georgia and northeast Florida with higher chances for storms occurring over southeast Georgia and for areas east of I-75. Daily high temperatures will rise up into the mid to upper 90s through midweek with overnight low temperatures dropping down into the mid 70s over inland areas and in the mid to upper 70s along the coastline. Heat index values during this period are expected to rise to be well above 100 Fahrenheit and potentially rising to near Heat Advisory levels.

LONG TERM /THURSDAY THROUGH MONDAY/

Main Highlights This Period:

- Isolated to Scattered Afternoon Thunderstorm Coverage.

- Heat Advisory Potential Each Day.

- Higher chances for thunderstorms on Friday. High pressure will move off to the east by Friday resulting in a more southerly and onshore flow going into the weekend, ahead of high pressure ridging moving over the forecast area from out of the Atlantic before the beginning of next week. Daily bouts of isolated to scattered thunderstorms are expected through the period, with convection forecasted to be more widespread on Friday and then diminishing over the weekend. Above average temperatures will continue through the end of the week and into the weekend with daily max temps rising into the upper 90s and heat index values reaching above 110 and likely reaching heat advisory levels during periods of peak heating.

AVIATION /00Z TUESDAY THROUGH 00Z WEDNESDAY/

Thunderstorms located along the Altamaha River in coastal southeast GA will likely impact SSI before 02Z, with wind gusts up to 30 knots and IFR visibilities during heavier downpours. Convection elsewhere near the FL/GA border will remain far enough away from JAX to preclude the need for VCTS this evening. Otherwise, VFR conditions should prevail at the regional terminals by 04Z. IFR to LIFR visibilities are then expected to develop overnight through the predawn hours on Tuesday at VQQ. Showers and thunderstorms are expected to impact portions of southeast GA and northeast FL on Tuesday afternoon and evening, mainly along the I-95 corridor as developing northwesterly flow aloft pushes convection southeastward. We have included a PROB30 group at SSI after 20Z for brief wind gusts up to 30 knots, along with MVFR visibilities during heavier downpours. Confidence in potential impacts at the northeast FL terminals on Tuesday afternoon remains too low for anything other than VCTS, generally after 18Z. VCTS was left out of the GNV TAF at this time, where VFR conditions will likely prevail throughout the period. Southerly surface winds of 5-10 knots at the SSI and SGJ coastal terminals should diminish to around 5 knots by 06Z, while speeds around 5 knots at the inland terminals will diminish towards 03Z. West-southwesterly surface winds will develop shortly after sunrise at the regional terminals, with speeds increasing to 5-10 knots by 15Z. The Atlantic sea breeze will move slowly inland on Tuesday afternoon, shifting surface winds to southeasterly at 10-15 knots at SGJ and southerly at 10-15 knots at SSI after 17Z.

MARINE

Strong thunderstorms containing gusty winds and frequent lightning strikes will continue to impact coastal southeast Georgia near the Altamaha River entrance through the evening hours before dissipating before midnight. Otherwise, Atlantic high pressure extending its axis across the northeast Florida waters tonight will shift south and westward on Tuesday as troughing takes shape over the southeastern states, with prevailing west-southwesterly winds expected developing on Tuesday morning. The afternoon sea breeze will shift winds to southeasterly over the near shore waters each day through the upcoming weekend, followed by southerly evening wind surges. Outside of thunderstorm activity, winds and seas will remain below Caution levels during the next several days. Another round of potentially strong thunderstorms will be possible on Tuesday afternoon and evening, mainly over the Georgia waters, with some impact possible for portions of the northeast Florida waters into the evening hours, mainly north of St. Augustine. Scattered mainly afternoon and evening thunderstorms will remain possible each day through the upcoming weekend.

Rip Currents: A lower end moderate risk may continue at the northeast FL beaches on Tuesday afternoon as breezy onshore winds develop following the passage of the sea breeze. Low surf heights will likely yield a low risk at the southeast GA beaches. A low risk is then expected from Wednesday through at least Saturday at area beaches as offshore winds and low surf heights prevail.

FIRE WEATHER

- Patchy High Afternoon Dispersions Beginning Tuesday

Light west to southwest winds will keep the Atlantic seabreeze near the coast each day, with lower thunderstorm coverage expected today through Wednesday and forecast to be around 20-40%. A few strong thunderstorms may produce gusty outflows with locally erratic winds.

Temperatures will rise into the mid 90s inland and lower to mid 90s at the coast today and Tuesday with peak heat index values rising to heat advisory levels to about 106-110 into midweek. Dispersions improve gradually today compared to Sunday. Patchy high inland dispersions expected Tuesday into Wednesday as mixing heights increase along with increasing westerly transport winds. Fog Potential: Significant fog development is not expected, with shallow, patchy fog late overnight limited to areas that receive locally heavy rainfall.

CLIMATE

Daily record high temperatures are possible by Thu-Fri:

Thursday, August 13th: KJAX: 99/2023 KAMG: 100/9999 KCRG: 96/2023

Friday, August 14th: KJAX: 99/2023 KGNV: 97/2023 KCRG: 98/2023

PRELIMINARY POINT TEMPS/POPS

AMG 75 95 76 95 / 10 40 20 20 SSI 80 93 79 95 / 10 60 30 30 JAX 75 96 75 94 / 10 60 40 50 SGJ 78 93 76 94 / 10 30 20 40 GNV 75 95 74 93 / 10 30 0 20 OCF 74 95 74 94 / 10 20 0 10

JAX WATCHES/WARNINGS/ADVISORIES

FL...None. GA...None. MARINE...None.