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 & Humid Weather Continues through Wednesday. Heat Advisories in Effect Area-Wide Today, with Heat Indices up to 112 Expected. Extreme Heat Watch & Heat Advisory Wed, Heat Indices of 110-115 Possible

- Isolated TStorms this Afternoon and Evening, Mostly South of I-10

- Strong to Severe Thunderstorms on Wednesday Afternoon and Evening. Damaging Wind Gusts of 40-60 mph, Frequent Lightning Strikes, and Localized

- Flooding Due to Heavy Downpours are Possible

- Numerous Mainly Afternoon & Evening TStorms Thursday through Monday. Daily Rounds of Heavy Downpours Could Result in Localized Flooding

UPDATE

Expanded coverage of isolated to widely scattered T'storms along and south of I-10 primarily east of highway 301 through the next few hours as late day convection sends outflows eastward towards the pinned Atlantic seabreeze. A quick T'storm should be brief from Jacksonville southward along US-17 and I-95 corridors with any wind gusts potentially up to around 40 mph.

The heat advisory will expire at 8PM. Otherwise no other changes to the forecast as an Excessive Heat Watch and Heat Advisory is in effect for Wednesday from 11AM to 8PM.

NEAR TERM /THROUGH TONIGHT/

Main Highlights For Today and Tonight:

- Near Record Heat with Dangerous Heat Indices through Wednesday.

- Heat Advisories Continue Area-Wide through 8 PM this Evening, with Peak Heat Index Values of 108-112 Degrees this Afternoon.

- Only Isolated Thunderstorms Possible for Inland Locations South of I-10 through this Evening.

Afternoon surface analysis depicts weakening high pressure (1014 millibars) positioned over western Gulf. Meanwhile, a surface trough was positioned across north central FL. Otherwise, a cold front was pushing southward through the Ohio Valley and the Upper Midwest, with another high pressure center (1019 millibars) spilling southward from Canada into the Great Lakes region in the wake of this front. Aloft..."heat wave" ridging remains centered over the southern Rockies and the southern Plains states, while troughing deepens from southeastern Canada through New England and the Mid- Atlantic states. A leftover mesoscale convective vortex (MCV)from overnight convection was weakening near Lake George in north central FL. Hazy skies remain in place across our region to the north of this feature, compliments of high altitude smoke that was emanating from numerous wildfires across the Pacific Northwest. Latest GOES- East derived Total Precipitable Water imagery indicates that PWATs across southeast GA were near late July climatology (1.8 -2 inches), while values were generally around or just 2 inches across the rest of our area.

Despite abundant moisture in place across northeast and north central FL, an unseasonably subsident air mass was limiting cumulus cloud growth for locations along and north of the Interstate 10 corridor. The inland moving Gulf sea breeze boundary has developed a few brief showers over southern portions of the Suwannee Valley and across north central FL, but updrafts have been weak and short- lived thus far. Temperatures at 19Z have soared to the mid to upper 90s at most inland locations, while the inland moving Atlantic sea breeze has lowered coastal temperatures across northeast FL to the upper 80s and lower 90s, with low to mid 90s prevailing for coastal southeast GA. Dewpoints were generally in the 70s, with heat index values values climbing to the 100-108 degree range.

Inland moving sea breezes will continue to battle the strongly subsident air mass that will remain in place across our area. Only isolated convection is expected this afternoon and evening, mainly for inland locations south of Interstate 10, where colliding sea, lake and river breezes could generate brief showers and possibly a thunderstorm or two. Hazy skies will continue through the overnight period as northwesterly flow deepens as troughing digs from the Ohio Valley through the Mid-Atlantic states. This digging trough will drive an associated cold front southward from the Ohio Valley through the Tennessee Valley and the southern Appalachians by sunrise on Wednesday. Our local pressure gradient will tighten somewhat ahead of this approaching front, with a southwesterly breeze keeping lows in the 75-80 degree range overnight, which will be near record warm minimum temperatures for July 29th (see "Climate" section below for details).

SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/

Main Highlights This Period:

- Areawide Heat Advisory Wednesday, with Extreme Heat Watch for coastal SE GA, coastal and inland NE FL

- Rounds of showers and thunderstorms, with strong to severe storms possible Wednesday and Thursday.

A frontal boundary will shifts southward towards the area on Wednesday. Ahead of the front, an unstable air mass with CAPE values from 2K to 3K J/kg over the area, will bring the potential for numerous to widespread strong to severe thunderstorms during the afternoon to early evening hours across SE GA and NE FL. The Storm Prediction Center (SPC) has highlighted most of the area either under a Marginal to Slight Risk of Severe Storms for Wednesday afternoon, with the Slight Risk extending from Alma, GA southwards towards the Suwannee Valley Region and eastward towards St. Augustine, FL. With any storms that do develop, the main hazards will likely be strong downbursts with winds ranging from 40 to 60 mph. An abundant amount of moisture aloft, we will likely also see heavy downpours that will bring flooding potential. By Thursday, the front will begin to stall near the FL/GA state line. Another day of showers and storms as the front will focus most of the activity south of its boundary across NE FL with On Thursday, with lower chances over interior SE GA. Similar to Wednesday, heavy downpours and strong downbursts will be possible for any showers and storms that develop during the afternoon to evening hours.

Temperatures on Wednesday will once again rise into mid to upper 90s across the area. In addition to the hot temperatures, dewpoints in the 70s will bring Heat Index values at or above Heat Advisory criteria, potentially into Extreme Heat Warning levels. At this time we have issued another Heat Advisory for all of SE GA and NE FL and an Extreme Heat Watch along the coastal and inland locations of NE FL for Wednesday. Thursday, a bit cooler with temperatures in the lower to mid 90s.

LONG TERM /FRIDAY THROUGH TUESDAY/

Main Highlights This Period:

- Daily rounds of mainly afternoon and evening thunderstorms, which may become strong to severe.

The stalled boundary will remain near the FL/GA state line into the weekend and begin to lift northward on Sunday. With an abundant amount of moisture and frontal convergence, there will continue to be a good coverage of convective development Friday through Monday as strong to isolated severe storms will be possible each afternoon. Temperatures will be above normal Friday. With convective activity expected over the weekend and into the upcoming week, temperatures will be cooler compared to the past couple of days.

AVIATION /00Z WEDNESDAY THROUGH 00Z THURSDAY/

VFR conditions will continue overnight and into the start of Wednesday with increasing coverage of thunderstorms Wednesday afternoon and potential for isolated strong to severe thunderstorms over the terminals. West southwest winds 6-10 knots will diminish some to around 5 knots inland while the Seabreeze will continue south to southeasterly winds 8-12 knots at SSI/SGJ/CRG through 03Z before resuming winds from the west southwest 5-10 knots.

Wednesday, a front will approach the area from the north with breezy west to southwest winds 10-15 knots with gusts to 20 knots across the Northeast FL TAF sites as the strong flow will not favor the Atlantic seabreeze moving onshore. Strong heating and an approaching wave aloft associated with the cold front will lead to increasing chances for thunderstorms. Have VCTS after 18Z Wednesday with PROB30 groups at this time for strong thunderstorms producing wind gusts up to 30 knots and IFR restrictions from very heavy downpours. Wind gusts in the afternoon may need to be adjusted upwards in subsequent forecasts due to potential for isolated severe storms.

There is potential for another round of storms after the end of the period from 00Z-06Z Wednesday night into very early Thursday. After the storms, VFR conditions will resume.

MARINE

Prevailing southwesterly winds are forecast today, with only isolated afternoon thunderstorms possible over the near shore waters adjacent to northeast Florida. Wind speeds will increase to Caution levels early this evening throughout our local waters, with these stronger speeds continuing through around sunrise on Wednesday. A frontal boundary will then sink into the Deep South late this week, with this feature becoming stationary during the weekend. Strong to severe thunderstorms will be possible well in advance of this front on Wednesday afternoon and evening, with stronger storms potentially producing damaging wind gusts, waterspouts, frequent lightning strikes, and torrential downpours. Scattered to numerous thunderstorms will continue across the northeast Florida waters on Thursday and Friday, with less coverage currently forecast for the Georgia waters. Waves of showers and thunderstorms will then overspread all of our local waters during the upcoming weekend. Outside of expected thunderstorm activity, southwesterly winds will prevail and will strengthen ahead of the approaching front beginning towards midweek, with Caution conditions likely through the upcoming weekend.

Rip Currents: Low to marginal moderate risk of rip currents is expected today and Wednesday at Northeast FL and Southeast GA beaches with surf/breakers of only 1-2 feet.

FIRE WEATHER

-Heat Indices in the Advisory to Heat Warning range for much of the area through Wednesday

-Patchy to areas of high daytime dispersions this week

-Isolated to Scattered Severe Storms Wednesday

A frontal zone across the Tennessee Valley will move into central Georgia on Wednesday and into southeast Georgia Thursday morning and slowly lift northward on Friday through the weekend. As the front moves into the region on Wednesday, it will support increased chances of thunderstorms mid week. Gusty and erratic winds can be expected in and near storms. Isolated to scattered storms may be strong to severe Wednesday afternoon and evening.

A hot airmass will continue the rest of today and on Wednesday with heat indices of 108 to 115. Heat advisories are in effect for the forecast area and Wednesday, with a extreme heat watch in effect for parts of the area Wednesday.

Given moderate transport wind speeds and elevated mixing heights, patchy to areas of high daytime dispersions are expected today through Friday, especially along and north of the I-10 corridor.

Fog Potential: Significant fog development is not expected during the next several mornings.

CLIMATE

Daily record high temperatures and record warm minimim temperatures at our designated climate sites on Tuesday and Wednesday:

July 28: KJAX: 104/1872 80/1885 KGNV: 100/2025 77/2014 KAMG: 100/2006 78/2014 KCRG: 100/2025 80/2014

July 29: KJAX: 101/2025 80/1877 KGNV: 100/2025 79/2025 KAMG: 99/2025 77/2017 KCRG: 101/2016 79/2017

PRELIMINARY POINT TEMPS/POPS

AMG 77 98 74 95 / 0 30 40 30 SSI 81 99 79 94 / 0 70 40 40 JAX 77 98 77 95 / 0 60 60 60 SGJ 78 97 77 93 / 10 50 30 80 GNV 77 95 77 92 / 20 30 40 80 OCF 77 93 77 91 / 10 30 70 80

JAX WATCHES/WARNINGS/ADVISORIES

FL...Extreme Heat Watch from Wednesday morning through Wednesday evening for FLZ021-023-024-030-031-035-120-124-125-132- 136-137-220-225-232-233-236-237-322-325-333-422-425-433- 522-533-633. Heat Advisory from 11 AM to 8 PM EDT Wednesday for FLZ038-138- 140-240-340. GA...Extreme Heat Watch from Wednesday morning through Wednesday evening for GAZ153-154-162-163-165-166-264-350-364. Heat Advisory from 11 AM to 8 PM EDT Wednesday for GAZ132>136- 149-151-152-250. MARINE...None.