textproduct: Jacksonville

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 to Isolated Severe Thunderstorms this Afternoon & Evening. Damaging Wind Gusts of 40-60 mph, Frequent Lightning Strikes and Heavy Downpours are Possible for Much of Our Area.

- Localized Flood Threat through Early this Evening as Waves of Downpours Impact Portions of Our Area.

- Oppressive Heat & Humidity Continues Area-Wide During the Next Several Days. Heat Advisories Issued for Most of our Area on Thursday, with Extreme Heat Warnings for the Coastal Counties in Southeast GA on Thursday Afternoon and Evening. Daily Heat Advisories Will Likely Continue for Much of Our Area into Next Week.

- Daily Scattered Afternoon and Evening Thunderstorms from Thursday through Tuesday.

NEAR TERM /THROUGH TONIGHT/

Main Highlights:

- Strong to Isolated Severe Thunderstorms through Early this Evening. Stronger Storms Will Be Capable of Producing Damaging Wind Gusts, Frequent Lightning Strikes, and Torrential Downpours.

- Localized Flood Threat through Early this Evening as Waves of Downpours Impact Portions of Our Area.

- Heat Advisories Remain Posted through 7 PM this Evening for Most of Our Area. Afternoon surface analysis depicts high pressure (1019 millibars) centered over the northeast Gulf. Aloft...deep- layered riding extending from Texas southeastward through the northeastern Gulf was producing deep and unstable northwesterly flow across our region, with a shortwave trough embedded within this flow exiting the Georgia coast near the Savannah River entrance. Latest GOES-East derived Total Precipitable Water imagery indicates that tropical moisture remains in place for locations along and north of the Interstate 10 corridor, where PWATS ranged from 2 - 2.25 inches. A slightly drier air mass exists to the south of the I-10 corridor, where PWATs were mostly in the 1.7 - 1.9 inch range. A convergent zone associated with the aforementioned shortwave trough was firing numerous thunderstorms across southeast GA and northeast FL, mainly for locations from Waycross southeastward to the I-10 corridor. Activity was progressing briskly southeastward at 20-30 mph. Outside of rain-cooled locations, oppressive heat and humidity continues, with temperatures at 18Z generally in the low and mid 90s, with dewpoints in the 70s driving heat index values up towards 105 degrees.

Outflow boundaries emanating from the convective zone should allow for thunderstorms to gradually shift southward as the afternoon progresses, with individual storm cells continuing to progress quickly southeastward. Strong to isolated severe thunderstorms will remain possible through the early evening hours as the focus for activity shifts south of the I-10 corridor. Plenty of instability and deep tropical moisture will keep the potential for wet microbursts in place, with storms also pulsing as outflow boundaries collide. Stronger convection will be capable of producing downburst wind gusts of 40-60 mph, along with frequent lightning strikes. Deep northwesterly flow will present a risk for training convection, and storms moving southeastward repeatedly over the same locations will increase the threat for localized flooding, especially for urban or normally flood prone locations. Outflow boundaries should also develop convection this afternoon across coastal southeast GA, where a few stronger storms will be possible as activity potentially interacts with a pinned Atlantic sea breeze boundary at the immediate coast.

Convection should dissipate over north central FL and the I-75 corridor by the mid-evening hours as shortwave energy moves further offshore of the Georgia coast. Debris cloud cover will thin out overnight, with viewing of the annual Perseid meteor shower improving during the predawn hours across our area from north to south. Otherwise, a warm and humid air mass will keep lows mostly in the mid to upper 70s.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/

Main Highlights This Period:

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

- Heat Index Values near Heat Advisory levels each day. Extreme Heat Warnings in place along the coastal counties in SE GA on Thursday.

A high pressure ridge will extend across southern FL this period, with a trough to the north. The ridge will weaken into Friday.

The flow on Thursday will prevail from the west, which will keep the east coast sea breeze from getting much further inland than the beaches. This will help the heat to push all the way to the beaches. The combination of heat and humidity will result in Heat Advisory level conditions across much of the area, but Heat Warning levels expected for coastal SE GA. Convection on Thursday will largely be driven by diurnal heating.

With the weaker high, the flow from the west will not be as strong, allowing the east coast sea breeze to push further inland. Convection on Friday will be driven by diurnal instability, and enhanced by sea breeze interactions. Temperatures will be similar Friday as Thursday, but a few degrees cooler at the beaches due to the sea breeze. Heat Advisory level conditions are anticipated for much of the area.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Main Highlights This Period:

- Warm temperatures continue over the weekend, with Heat Advisories likely on Saturday.

- Isolated to scattered thunderstorms each afternoon evening, which could become strong.

A cold front will move south into the area Saturday, then stall near the FL/GA line through Sunday, before weakening over the area early next week. Another front will approach from the north during the middle of next week.

Afternoon and evening convection will be isolated to scattered this period. The highest chance this period will be on Sunday, due to the front being over the area.

Above average temperatures are expected throughout this period.

AVIATION /18Z WEDNESDAY THROUGH 18Z THURSDAY/

Strong to isolated thunderstorms will continue to impact the Duval County terminals through around 20Z, with brief wind gusts up to 45 knots possible within stronger storm cells, with IFR to LIFR visibilities likely during heavier downpours. Several rounds of strong convection will be possible through around 22Z. Activity will gradually shift southward and eastward, likely impacting SGJ and SSI after 19Z and potentially GNV after 21Z, where brief wind gusts up to 35 knots and IFR visibilities during heavier downpours are possible through around 01Z. Convection should shift south of the GNV terminal by 02Z, with VFR conditions then expected to prevail overnight at the regional terminals. Periods of MVFR visibilities will be possible overnight at VQQ, but confidence was too low to include at this time. Another round of potentially strong convection will likely impact our region on Thursday afternoon after the conclusion of this TAF period. Outside of convection, west or southwesterly surface winds will remain sustained around 10 knots through around 00Z. Surface winds will then shift to westerly around 5 knots overnight, followed by winds shifting to west-northwesterly towards sunrise, with speeds increasing to 5-10 knots by 14Z Thursday.

MARINE

High pressure positioned over the eastern Gulf will weaken on Thursday as troughing develops over the southeastern states. Westerly winds will prevail during the next several days, with the sea breeze shifting winds to southeasterly or southerly over the near shore waters each afternoon, followed by southerly evening wind surges that may briefly increase speeds to near caution levels before subsiding after midnight. Strong to isolated severe thunderstorms may impact portions of our local waters this afternoon through early this evening, with stronger storms capable of producing damaging wind gusts, frequent lightning strikes, and locally rough seas. Scattered mainly afternoon and evening thunderstorms will remain possible each day through the upcoming weekend.

Rip Currents: Prevailing offshore winds during the overnight and morning hours will keep surf heights below 2 feet at area beaches outside of thunderstorm activity, maintaining a mostly low risk during the next several days.

FIRE WEATHER

- Heat Headlines in Effect.

High pressure ridge will be located across southern FL with a trough to the north through Friday. A front will move south into the area Saturday, before stalling near the FL/GA line Sunday. The boundary will dissipate early next week. Another front will approach toward the middle of next week. Isolated to scattered thunderstorms each afternoon and evening. Temperatures will be above average this period, with heat indices near or above advisory levels each day. 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 from Thursday through Saturday:

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

Friday August 14th: KJAX: 99/2023 KGNV: 97/2023 KAMG: 101/2023 KCRG: 98/2023

Saturday August 15th: KJAX: 99/1956 KGNV: 100/1918 KAMG: 99/1995 KCRG: 97/9999

PRELIMINARY POINT TEMPS/POPS

AMG 76 96 77 96 / 10 30 10 30 SSI 79 96 79 95 / 20 30 10 20 JAX 76 95 76 95 / 20 40 10 40 SGJ 78 94 77 94 / 30 40 10 30 GNV 77 95 75 95 / 60 50 30 60 OCF 76 95 75 96 / 50 50 20 40

JAX WATCHES/WARNINGS/ADVISORIES

FL...Heat Advisory until 7 PM EDT this evening for FLZ021-023-024- 030-031-035-038-120-124-125-132-136>138-140-220-225-232- 233-236-237-240-322-325-333-340-422-425-433-522-533-633. Heat Advisory from 11 AM to 8 PM EDT Thursday for FLZ021-023- 024-030-031-035-038-120-124-125-132-136>138-140-220-225- 232-233-236-237-240-322-325-333-340-422-425-433-522-533- 633. GA...Heat Advisory until 7 PM EDT this evening for GAZ152>154-162- 165-166-264-350-364. Heat Advisory from 11 AM to 8 PM EDT Thursday for GAZ132>136- 149-151-152-162-163-250-264-350-364. Extreme Heat Warning from 11 AM to 8 PM EDT Thursday for GAZ153-154-165-166. MARINE...None.