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. Heat Advisories & Extreme Heat Warnings Possible Tuesday 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,

- 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

Another hot day will be in store today with the overall synoptic setup changing overall little compared to the last few days as high pressure ridging remains in place aloft. The main change that is noteworthy revolves around a weakening front/trough that will drop southward throughout the day today, settling just north of the region tonight. This will increase the pressure gradient slightly, while also inducing more of a continental west to northwest flow across inland GA. These features, combined with slightly drier PWATs moving into parts of southern GA associated with the troughing feature, will limit convection for most areas across southeast GA counties, while more scattered activity will be found across northeast FL and the potential for stronger storms being towards the nearly pinned sea breeze. 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.

As mentioned above, certainly will be another hot day for many given the subsidence aloft and west to southwest flow. Heat Advisories are in effect for the entirety of the area, and Extreme Heat Warning is in effect for Glynn and Camden. Peak heat indices will be around 108 to 112 in heat advisory areas, and 113-115 for parts of Glynn and Camden Counties. High temperatures will be generally in the mid to upper 90s, with a few readings around 100 possible over inland GA given the slightly drier conditions and more time in the sun.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/

Main Highlights This Period:

- 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 "Heat Wave" ridging retrogrades towards the Desert Southwest and broad troughing digs across the Great Lakes and New England. 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 rising above 2.25 inches across coastal southeast GA, northeast and north central FL. A drier air mass may begin to filter into interior southeast GA by late afternoon, keeping widespread convective activity confined to northeast and north central 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 storms to "pulse", with 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, with another day of Extreme Heat conditions possible for coastal southeast GA and possibly the I-95 corridor in northeast FL, where Heat Index Values will peak in the 113-115 degree range. Heat indices elsewhere will peak in the Advisory range of 108-112 degrees, except for locations north and west of Waycross, where the incoming drier air mass may keep values closer to 105 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 on Wednesday as west-northwesterly flow advects a drier air mass 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 through the 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, northeast and north central 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:

- 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 "Heat Wave" ridging amplifies over the Rockies and the Desert Southwest. 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 from the Okefenokee Swamp southward. Near record heat will otherwise 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 /12Z MONDAY THROUGH 12Z TUESDAY/

VFR is expected to prevail through the morning hours. Westerly flow will generally keep the Atlantic sea breeze near the coast, with wind shifts only included at SSI and SGJ at this time. 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 accordingly late in the forecast period.

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 during the afternoon 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, with southwesterly winds surging ahead of this boundary on Tuesday evening possibly bringing speeds up to near Caution levels. Coverage of afternoon and evening showers and thunderstorms will shift to the northeast Florida waters on Wednesday and Thursday.

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 Today

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. Extreme Heat Warnings are in effect today for coastal southeast Georgia, with Heat Advisories posted elsewhere from 11 AM this morning through 8 PM this evening. Otherwise, scattered afternoon and evening thunderstorms are forecast for locations south and east of Waycross and Brunswick in southeast Georgia and for all of northeast and north central Florida today. West-northwesterly transport winds will shift to west or west-southwesterly this afternoon, with surface winds shifting to south or southeasterly at coastal locations during the early to mid afternoon hours as the Atlantic sea breeze moves slowly inland. 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 and north central 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 / 10 0 40 20 SSI 96 80 98 79 / 20 10 40 40 JAX 96 77 96 77 / 40 20 60 40 SGJ 95 78 95 78 / 50 20 60 50 GNV 96 77 94 77 / 50 10 60 30 OCF 95 77 95 78 / 40 10 70 30

JAX WATCHES/WARNINGS/ADVISORIES

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