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

- Dangerously HOT Weather Continues this Week. Heat Advisory/Extreme Heat Warning this Afternoon & Evening and Tuesday. Heat Advisories & Extreme Heat Warnings Possible Wednesday through Friday

- Scattered Thunderstorms Today, Isolated Strong Storms Possible. Main Impact Area: Northeast & North Central FL. Strong Storm Hazards: Wind Gusts of 35 - 45 mph, Frequent Lightning Strikes, Heavy Downpours

- Scattered to Numerous Afternoon & Evening TStorms Tues Sat. Strong to Isolated Severe Storms are Possible Each Day, Mainly Along the I-95

NEAR TERM /THROUGH TONIGHT/

Main Highlights through Tonight:

- Heat Advisory Area-Wide Today, Extreme Heat Warning Coastal GA - Isolated Strong Thunderstorms this afternoon and early evening, Mainly Across Northeast FL

Hot and humid conditions continue with high pressure ridging aloft and a very moist airmass in the low-mid levels with the 12Z KJAX sounding measuring a PWAT of 2.51 in. Generally westerly flow today will keep the Atlantic sea breeze pinned to the Atlantic coast this afternoon. Isolated showers and storms develop along the Gulf sea breeze early this afternoon with activity increasing in coverage across NE FL as it approaches the Atlantic sea breeze. Some mixing out in inland SE GA will limit convection this afternoon. Best chances for rain and stronger storms will be along the sea breeze merger in the St Johns river basin and I-95 corridor later this afternoon into early evening. Torrential rainfall and isolated strong to marginally severe wind gusts will be the primary hazards given the pulse type of showers and thunderstorms expected and pretty warm temperatures aloft.

Extreme Heat Warnings are in effect for Glynn and Camden with Heat Advisories in effect elsewhere across NE FL and SE GA. Peak heat indices will be around 108 to 112 F in heat advisory areas, and 113 F for parts of Glynn and Camden Counties. High temperatures will be generally in the mid to upper 90s. Overnight lows will be in the 70s.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/

Main Highlights This Period (Tuesday and Wednesday):

- Near Record Heat and Seasonably High Humidity Will Keep Dangerously High Heat Index Values in Place Area-Wide on Tuesday

- Strong to Isolated Severe Thunderstorms Possible on Tuesday Afternoon & Evening, Mainly for Locations South and East of Waycross

- Drier Air Mass Filters into Southeast GA on Wednesday, with Scattered to Numerous Afternoon and Evening Thunderstorms Possible South of Interstate 10

West-northwesterly flow aloft will prevail across the southeastern states on Tuesday and Wednesday as ridging retrogrades towards the West and broad troughing digs across the Eastern US states. This trough will continue to push a frontal boundary slowly southward towards our area by midweek. Deeper moisture will pool downstream of this boundary across our region on Tuesday, with PWATs well above 2 inches across coastal southeast GA and, northeast FL. A drier air mass may begin to filter into inland southeast GA by late afternoon, keeping widespread convective activity confined to northeast FL. However, the presence of the approaching front should still fire off scattered showers and thunderstorms during the early to mid afternoon hours across southeast GA. Strong to isolated severe thunderstorms will be possible along the I-95 corridor during the late afternoon and early evening hours as activity along the dominant eastward moving Gulf sea breeze boundary encounters a pinned Atlantic sea breeze boundary, likely causing stronger storms capable of producing downburst winds of 40-60 mph, frequent lightning strikes, and locally heavy downpours

Breezy west-southwesterly low level flow will delay the development of the Atlantic sea breeze at coastal locations, allowing near record heat to extend all the way to area beaches. High temperatures will climb to the 95-100 degree range before convection increases in coverage and intensity, and Extreme Heat Warnings have been posted for coastal SE GA and all of NE FL, where Heat Index Values will peak in the 113-115 degree range. Heat indices elsewhere across inland SE GA will peak in the Advisory range of 108-112 degrees. Convection should shift eastward and offshore before midnight on Tuesday night, with lows generally falling to the mid and upper 70s.

PWATs will fall below 1.5 inches throughout southeast GA late Wed afternoon as west-northwesterly flow advects a drier air mass aloft southward towards the I-10 corridor. However, the frontal boundary will stall near or just north of the Altamaha River, and highs will soar to around 100 for inland southeast GA, with mid to upper 90s expected elsewhere. Dewpoints falling into the mid/upper 60s in the drier air mass across inland southeast GA should keep maximum heat index values below Heat Advisory criteria, with values elsewhere across coastal southeast GA and northeast FL likely reaching Heat Advisory criteria once again. Scattered to numerous afternoon and evening thunderstorms will likely be confined to locations south of I-10, with a few stronger storms again possible along the I-95 corridor south of Jacksonville. A few storms may linger across north central FL on Wednesday evening, with fair skies forecast elsewhere and lows again only falling to the mid and upper 70s.

LONG TERM /THURSDAY THROUGH SUNDAY/

Main Highlights This Period (Thursday through Sunday):

- Near Record Heat and Dangerously High Heat Indices Continue on Thursday and Friday.

- Scattered to Numerous Afternoon and Evening Thunderstorms Each Day from Friday through the Upcoming Weekend

Troughing aloft will slowly dig over the eastern half of the nation as ridging amplifies over the Western US. This weather pattern will keep a wavy frontal boundary in place over the Deep South, with deep- layered southwesterly flow prevailing locally. The unseasonably dry air mass that will filter into southeast GA on Wednesday will linger on Thursday, keeping scattered afternoon and evening thunderstorms mostly confined to areas across NE FL. Near record heat will continue with highs again climbing to the 95-100 degree range at most locations. Dewpoints will again fall through the 60s across southeast GA, keeping heat index values below Advisory levels, while values elsewhere across coastal southeast GA, northeast and north central FL again reach the 108-112 degree range. Convection may linger through the mid-evening hours on Thursday along the I-95 corridor and north central FL, with fair skies after midnight again yielding lows in the mid to upper 70s at most locations.

Friday will likely be a transition to a more typical stormier weather pattern as deepening southwesterly flow pools tropical moisture along and downstream of a wavy stationary frontal boundary that will remain in place across the southeastern states. Highs may still soar to the mid and upper 90s, with heat index values rising to at least Heat Advisory levels for much of our area. Scattered to numerous afternoon and evening thunderstorms should develop across our region as PWATs likely rise above 2 inches at most locations. Scattered to numerous afternoon and evening thunderstorms are then expected area-wide during the upcoming weekend, with convective initiation during the early to mid afternoon hours likely keeping temperatures in the low to mid 90s, with heat indices staying below Heat Advisory thresholds for most of our area. Lows in the low to mid 70s are forecast inland, while mid to upper 70s continue at coastal locations.

AVIATION /18Z MONDAY THROUGH 18Z TUESDAY/

Westerly flow will generally keep the Atlantic sea breeze near the coast, with wind shifts to southwesterly only included at SSI and SGJ for this afternoon. Convection is expected to be found mainly across northeast FL, and have included PROB30 groups for all sites accordingly except SSI where chances are too low to include any TS mention at this time. Convection will start to wane after 00Z, with VFR returning overnight.

MARINE

High pressure extending from the Bahamas westward across the Gulf will gradually weaken this week as a frontal boundary sags southward over the southeastern states. Westerly winds will prevail during the next several days, with winds over the near shore waters shifting to southerly and increasing during the afternoon and evening hours as the Atlantic sea breeze shifts slowly inland. Coverage of afternoon and evening showers and thunderstorms will increase on Tuesday ahead of the approaching frontal boundary. Showers and thunderstorms will shift to the northeast Florida waters on Wednesday and Thursday as the front stalls and dissipates.

Rip Currents: Prevailing offshore winds will strengthen slightly today, though risk will remain low to moderate that will likely continue through the end of the work week at all area beaches.

FIRE WEATHER

HEAT ADVISORIES AND EXTREME HEAT WARNINGS IN EFFECT THIS - Afternoon And Again On Tuesday

MARGINALLY HIGH DAYTIME DISPERSIONS POSSIBLE ACROSS INLAND - Southeast Georgia On Tuesday And Wednesday

Near record heat and seasonably high humidity values will result in dangerously high heat index values nearly area-wide this week. Otherwise, scattered afternoon and evening thunderstorms are expected this afternoon and evening, mainly across Northeast Florida. Elevated mixing heights will yield good daytime dispersion values at inland locations this afternoon, with fair values forecast at coastal locations.

A similar weather pattern will prevail on Tuesday, with scattered to numerous afternoon and evening thunderstorms possible. Elevated mixing heights and slightly stronger westerly transport winds may create marginally high daytime dispersion values across portions of inland southeast Georgia on Tuesday and Wednesday afternoons. A drier air mass will filter into southeast Georgia on Wednesday and Thursday, limiting chances for afternoon and evening showers and thunderstorms. Scattered to numerous afternoon and evening thunderstorm coverage will shift southward to northeast Florida by Wednesday and Thursday.

Fog Potential: Significant fog formation is not expected. Gusty and erratic winds are possible within stronger thunderstorms.

CLIMATE

Near record high temperatures are possible at some of our designated climate sites during the next several days:

Monday, August 17: KJAX: 99/1954 KGNV: 97/1954 KAMG: 104/1995 KCRG: 97/2005

Tuesday, August 18: KJAX: 98/1954 KGNV: 98/1954 KAMG: 105/1995 KCRG: 96/2023

Wednesday, August 19th: KJAX: 99/1900 KGNV: 100/1954 KAMG: 103/1995 KCRG: 97/2010

Thursday, August 20th: KJAX: 101/1900 KGNV: 99/1900 KAMG: 104/1995 KCRG: 98/2016

PRELIMINARY POINT TEMPS/POPS

AMG 97 77 98 76 / 20 0 20 0 SSI 96 80 95 79 / 20 0 40 20 JAX 97 78 97 78 / 30 10 60 30 SGJ 95 78 95 78 / 40 20 50 20 GNV 96 77 94 78 / 30 20 60 20 OCF 95 77 94 78 / 30 20 50 30

JAX WATCHES/WARNINGS/ADVISORIES

FL...Heat Advisory until 8 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. Extreme Heat Warning from 11 AM to 8 PM EDT Tuesday 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 8 PM EDT this evening for GAZ132>136-149- 151-152-162-163-250-264-350-364. Extreme Heat Warning from 11 AM to 8 PM EDT Tuesday for GAZ153- 154-162-165-166. Heat Advisory from 11 AM to 8 PM EDT Tuesday for GAZ132>136- 149-151-152-163-250-264-350-364. Extreme Heat Warning until 8 PM EDT this evening for GAZ153- 154-165-166. MARINE...None.