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. Extreme Heat Warning and Heat Advisories Today from 11 AM 8 PM. Heat Index Values Peak in the 108-115 F Range this Afternoon. Heat Advisories & Extreme Heat Warnings Possible Wednesday through Friday

- Scattered to Numerous TStorms Each Afternoon & Evening through Sunday. Main Impact Areas through Thursday: Northeast and North Central FL. Strong Storms are Possible Each Day, Mainly Along the I-95 Corridor. Primary Hazards: Wind Gusts of 40-55 mph, Frequent Lightning Strikes, and Heavy Downpours

NEAR TERM /THROUGH TONIGHT/

Main Highlights through Tonight:

- Dangerously Hot and Humid Weather Peaks in Intensity Today, with Near Record High Temperatures Possible. Extreme Heat Warnings and Heat Advisories are in Effect from 11 AM - 8 PM Today. - Strong Thunderstorms Possible Late this Afternoon and Evening, Mainly Across Northeast and North Central FL.

Early morning surface analysis depicts high pressure (1019 millibars) extending from the Bahamas westward across the FL peninsula and through central portions of the Gulf. Meanwhile, a frontal boundary extends from New England south-southwestward across the Mid-Atlantic states and the Tennessee and lower Mississippi Valleys. Aloft..."Heat Wave" ridging centered over northern Texas continues to extend its axis southeastward along the northern Gulf coast and through our area. A shortwave trough was riding the northern periphery of this ridge across the Tennessee Valley. Otherwise, deep troughing over Hudson Bay, Canada was digging slowly southward across the Upper Midwest, Great Lakes, and New England. Latest GOES-East derived Total Precipitable Water imagery indicates that deep tropical moisture resides across most of our region, with PWATs ranging from 1.9 - 2.2 inches. A slightly drier air mass was advecting southeastward across eastern portions of GA, where PWAT values just north of the Altamaha River were in the 1.6- 1.8 range. Fair skies prevail throughout our region, with a light west- southwesterly breeze keeping temperatures at 08Z in the upper 70s and lower 80s nearly area-wide, with muggy dewpoints in the mid to upper 70s.

"Heat Wave" ridging over Texas will begin to slowly retrograde westward towards the Four Corners region of the Desert Southwest later today and tonight, allowing a broad trough to gradually take shape over the Deep South. West-northwesterly low and mid level flow on the periphery of this ridge will advect a slightly drier air mass into interior portions of southeast GA today, while deep tropical moisture will prevail elsewhere downstream of a decelerating frontal boundary that will be entering the southeastern states. This slightly drier air mass should limit convective development for locations from Waycross northward in southeast GA this afternoon, and dewpoints falling to near 70 late in the afternoon as the drier air mass mixes down to the surface. Plenty of sunshine will boost highs to near 100 across most of southeast GA, with maximum heat indices climbing to near 110 for interior southeast GA, where Heat Advisories are in effect from 11 AM through 8 PM.

West-northwesterly low and mid level flow will delay the development of the Atlantic sea breeze to the early to mid-afternoon hours at coastal locations, with this boundary making slow progress towards the I-95 corridor late this afternoon. Dewpoints rising to the mid and upper 70s following the passage of the sea breeze should provide for Extreme Heat Warning conditions across Glynn and Camden Counties later this afternoon and evening, where heat index values could peak near 115 degrees, prompting the issuance of Extreme Heat Warnings. The deep tropical air mass over northeast and north central FL should keep dewpoints in the mid to upper 70s, which will combine with afternoon highs in the 95-100 degree range to create peak heat index values of 113-115 degrees, prompting Extreme Heat Warnings from 11 AM - 8 PM.

Weak shortwave energy riding the periphery of the "Heat Wave" ridge should enter our area late this afternoon and evening. Although relatively mild temperatures aloft could temper storm intensity somewhat, plenty of tropical moisture located across northeast and north central FL should allow for scattered convection to develop along mesoscale boundaries such as the inland moving Gulf and Atlantic sea breezes during the mid and late afternoon hours. Convection should increase in coverage and intensity late this afternoon and early this evening across much of northeast and north central FL as convective outflows and other mesoscale boundaries collide, with a few storms pulsing and likely becoming at least briefly strong, with wet microburst potential that could produce wind gusts of 40-55 mph, along with frequent lightning strikes and locally heavy downpours.

Shortwave energy entering out region late this afternoon and evening could keep convection going well into the evening hours across northeast and north central FL, with convective outflows potentially igniting widely scattered convection during the early to mid evening hours across southeast GA, generally for locations south and east of Waycross. Convection should then dissipate towards or just after midnight across our region, followed by debris cloud cover thinning out during the predawn hours. Lows tonight should be slightly cooler than what we are experiencing this morning, as values mostly fall to the mid and upper 70s.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/

Main Highlights This Period (Wednesday and Thursday):

- Greatest chance for thunderstorms this period over NE FL during the afternoon and evening hours, with a few strong storms possible

- Heat Advisories may be needed both Wednesday and Thursday

An area of low pressure will be centered over the Carolinas this period, with a cold front extending across southern GA. A weak trough will extend south from it across region.

A prevailing flow from the west is expected Wednesday, with the east coast sea breeze pushing to around the I95 corridor. Drier air will advect into SE GA with the front. With the drier air over SE GA, the greatest chance for convection will be over southern portions of NE FL, especially closer to the east coast sea breeze.

On Thursday, the prevailing low level flow will be from the southwest and weaker, which will allow the east coast sea breeze to push further inland. It will not be as dry over SE GA on Thursday, so chances for convection will extend a little further north. With the sea breeze moving further inland, the focus for highest chances will also move further inland.

Temperatures will continue above average this period, and heat advisories may be needed.

LONG TERM /FRIDAY THROUGH MONDAY/

Main Highlights This Period (Friday through Monday):

- 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

An area of low pressure will remain over the Carolinas this period, with a frontal boundary extending southwest from it. This front is expected to largely stay north of SE GA this period. A high pressure ridge will extend across south FL.

This pattern will result in a prevailing flow from the southwest. With this flow, the east coast sea breeze will have a hard time making it much further inland than the I95 corridor.

An upper trough will be over the region throughout this period, with waves moves through it. The upper energy will help to create greater instability over the area. The strongest upper wave moves through Saturday, which is when the greatest chance for convection is forecast.

Temperatures will be near to a little above average this period.

AVIATION /12Z TUESDAY THROUGH 12Z WEDNESDAY/

VFR conditions will prevail at the regional terminals through at least 18Z. Showers and thunderstorms are expected to increase in coverage and intensity near the northeast FL terminals after 18Z through around 02Z. Have PROB30/TEMPO groups at the northeast FL terminals to account for brief gusts up to 30 knots and IFR visibilities during heavier downpours. Confidence in convective coverage across southeast GA this afternoon and evening remains too low to include anything other than vicinity shower coverage at this time. Convection may linger through around 02Z Wednesday at the northeast FL terminals, with VFR conditions then expected overnight. Westerly winds 5-10 kts prevail today outside of storms. The Atlantic sea breeze will likely not move onshore until after 18Z, with the passage of this boundary shifting surface winds to south- southwesterly at SGJ and SSI.

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 couple of 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 later this afternoon and evening, mainly across the northeast Florida waters. Scattered to numerous afternoon and evening thunderstorms will mostly be confined to the northeast Florida waters on Wednesday and Thursday, followed by coverage gradually increasing across the Georgia waters from Friday through the upcoming weekend as the frontal boundary stalls near our area.

Rip Currents: Prevailing offshore winds and low surf heights will keep a low risk in place through at least midweek at area beaches. Offshore winds will decrease slightly by Thursday and Friday, allowing the afternoon sea breeze to create breezy onshore winds that may result in a lower end moderate risk at the northeast FL beaches on Thursday and Friday.

FIRE WEATHER

- Heat Advisories And Extreme Heat Warnings In Effect Today

- Patchy High Daytime Dispersions Se Ga Today And Wednesday

The region will be between high pressure to the south, and a frontal zone to the north this period. Thunderstorms will be in the forecast each afternoon and evening this period. The highest chance for storms will be on Saturday. It will be an abnormally hot week, with readings returning to more seasonal levels over the weekend.

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:

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

Friday, August 21st: KJAX: 101/1900 KGNV: 99/1983 KAMG: 100/1980 KCRG: 99/2016

PRELIMINARY POINT TEMPS/POPS

AMG 98 77 99 74 / 20 20 10 0 SSI 97 80 97 80 / 20 10 10 0 JAX 98 78 97 76 / 50 30 40 10 SGJ 96 79 96 77 / 60 20 50 10 GNV 96 78 95 75 / 50 30 60 20 OCF 95 78 96 76 / 40 30 70 10

JAX WATCHES/WARNINGS/ADVISORIES

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