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

- Scattered Afternoon & Evening Thunderstorms through Friday. Hazards: Wind Gusts of 35-45 mph, Frequent Lightning & Heavy Downpours

- Increasing Coverage of Afternoon & Evening Thunderstorms Saturday

- Waves of Downpours & Thunderstorms Possible on Sunday and Monday. Heavy Rainfall & Localized Flooding Possible for Northeast & North Central FL

- Moderate Rip Current Risk at the Northeast FL Beaches

- Heat Advisory Conditions Possible Towards the Middle of Next Week

NEAR TERM /THROUGH TONIGHT/

Main Highlights Today and Tonight:

- Typically Hot and Humid Summertime Weather Continues.

- Scattered Afternoon and Early Evening Showers and Thunderstorms Today.

Early morning surface analysis depicts high pressure (1021 millibars) situated just south of the northern Gulf coast. Meanwhile, a frontal boundary that was in place over the southeastern states was dissipating. Aloft..."Heat wave" ridging extends from the Upper Midwest southeastward across the Carolinas, with this feature flattening as troughing digs over the Great Lakes and New England. Beneath this ridge, a Tropical Upper Tropospheric Trough (TUTT) was spinning slowly northwestward across south FL and the FL Keys towards the southeast Gulf. Mid and high altitude debris cloudiness was gradually thinning out across our area, with light west winds keeping temperatures generally in the 75-80 degree range as of 08Z, with dewpoints mostly in the low to mid 70s.

Ridging positioned over the Carolinas will continue to flatten as the aforementioned "TUTT" feature over south FL and the FL Keys slowly sharpens while drifting northwestward into the southeast Gulf by early Friday. Low and mid level northwesterly flow will otherwise continue through tonight as surface ridging just south of the northern Gulf coast slowly retrogrades westward. Seasonably hot and humid conditions will continue today, with inland highs climbing into the mid 90s, with a slightly delayed Atlantic sea breeze allowing highs to again reach the lower 90s at coastal locations. Heat index values will likely peak just below Heat Advisory criteria, with values generally in the 102-107 degree range this afternoon.

Seasonable moisture levels should activate scattered convective development during the early to mid afternoon hours along mesoscale boundaries such as the inland moving Atlantic and Gulf sea breezes, with slightly higher PWATs compared to Wednesday perhaps increasing coverage across north central FL and the St. Johns River basin late this afternoon and early this evening as mesoscale boundaries collide near the U.S. Highway 17 and 301 corridors. A few storms may pulse as these boundaries collide, but relatively mild mid-level temperatures and weak lapse rates should keep any stronger storms that develop below severe limits. Stronger storms could produce downburst winds of 35-45 mph, along with frequent lightning strikes and heavy downpours, as storm motion today should be rather slow.

Convection may drift further inland across the U.S.-301 corridor early this evening, but coverage should quickly diminish after sunset. Debris cloud cover will thin out towards midnight, with light low level westerly flow keeping lows mostly in the mid 70s inland and the upper 70s to around 80 at coastal locations.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/

Main Highlights During Friday and Sunday:

- Heavy Rain and Localized Flood Concerns for NE FL this Weekend - Daily bouts of showers and storms

Increasing afternoon thunderstorms is expected Friday as deep pooling moisture plasters the area. One factor for the Friday uptick in coverage will be the cooling temperatures aloft associated with a a tropical upper tropospheric trough closes off into upper low. The progression of the mid/upper level feature will likely bring numerous showers and thunderstorms across the NE FL zones Friday afternoon, initiating along the sea breezes. Due to the northwesterly flow the zone of sea breeze convergence will be generally along the US 301 corridor Friday.

As the upper low closes, it'll retrograde a bit farther northwest and anchor over the northeastern Gulf where it will sit until a northern stream trough dips across the eastern US, helping the low eject northeastward through Sunday. This feature will be the focus as a weak surface low may be reflected beneath the closed low, which may gradually become tropical in nature as it lifts northeastward on Sunday. The Nat'l Hurricane Center maintains only a 20% chance of tropical development with the latest guidance more pessimistic at surface low development.

Whether a surface low develops or not, a tropical-like airmass will be in place especially for areas along the I-75 corridor. Heavy rain concerns will be the primary focus over the weekend with potential for localized flash flooding, mainly for NE and north central FL zones.

Otherwise, seasonable summer heat will continue through the weekend, though cloud cover will associated with the low may cap highs in the upper 80s by Sunday. For Friday and Saturday highs in the low to mid 90s and heat index peaking in the 102-107 range is expected each afternoon.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

Main Highlights For Next Week:

- Scattered to Numerous Afternoon Thunderstorms - Potential heat advisory conditions by the middle of next week

If the the upper low lifts away according to the latest guidance, a west to southwesterly flow trailing it and deep moisture will keep chances fairly high 50-70% each afternoon through the first half of next week. Heat will will also build gradually through next week as upper ridging begins to nose in from the west-northwest. As peak temperatures push back into the mid 90s, the heat index may begin to approach Heat Advisory levels by the middle of next week.

AVIATION /12Z THURSDAY THROUGH 12Z FRIDAY/

VFR conditions will continue through the TAF period into the afternoon before scattered thunderstorms becoming more numerous mid to late afternoon will bring restrictions MVFR visibility from heavy downpours, brief gusty winds as the Atlantic seabreeze pushes past the coastal and Duval terminals and the Gulf seabreeze near GNV mid to late this afternoon.

Surface high pressure west of the area along the northern Gulf coast will keep light northwest to west northwest winds through the late morning 5-8 knots into midday hours with scattered diurnal cumulus clouds developing around 2.5 kft. Cloud bases will rise to around 4.0 to 5.0 kft by early afternoon as the Atlantic Seabreeze moves onshore by 17-18Z at SGJ/SSI, then to CRG and JAX 19-21Z. Continuing PROB30 groups primarily mid to late afternoon mostly for MVFR visibility from heavy rainfall with storms with the window starting earlier at the coast and a bit later at GNV and VQQ through 02Z. Wind gusts up to 25 knots possible in storms. Thunderstorms will dissipate with loss of heating after 00Z, lingering inland through 02Z. Lingering mid to high level leftover storm clouds and isolated showers with VCSH coverage will continue through 03-05Z with light southerly winds turning southwesterly around 5 knots along coast and trending calm inland after 06Z.

MARINE

High pressure centered over the Gulf will maintain a prevailing northwesterly wind flow across our local waters through Friday, with the afternoon sea breeze shifting winds to east-southeasterly over the near shore waters, followed by a slight southerly evening wind surge throughout our waters after sunset. Showers and thunderstorms developing along the inland moving sea breeze late this afternoon may shift back over the near shore waters early this evening before dissipating. A similar weather pattern will continue on Friday, with mostly dry weather continuing offshore. Surface troughing will then develop over the southeastern states on Saturday, shifting prevailing winds to southwesterly, with southerly evening wind surges this weekend likely bringing at least Caution level wind speeds to our local waters. Surface troughing will continue to sharpen on Sunday and Monday, with weak low pressure possibly developing over the northeast Gulf. The National Hurricane Center has maintained a low chance, or 20 percent, of weak tropical cyclone formation in the northeast Gulf. Showers and thunderstorms will increase in coverage this weekend, and this weak low pressure center may then progress northeastward across our local waters early next week.

Rip Currents:

Onshore winds developing this afternoon behind the inland moving sea breeze could create a lower end moderate risk at the northeast FL beaches, where surf heights may increase to around 2 feet. Meanwhile, low surf heights at the southeast GA beaches should maintain a low risk through at least Friday. Southerly wind surges during the evening hours this weekend may build surf heights to 2-3 feet at the northeast FL beaches and to around 2 feet at the southeast GA beaches, yielding a moderate risk at all area beaches.

FIRE WEATHER

- Patchy High Dispersions Over Inland Northeast Fl Today

Prevailing northwesterly transport and surface winds will keep the Atlantic sea breeze pushing beyond the I-95 corridor this afternoon. Due to the breezy northwesterly flow, patchy inland dispersions are likely, with high dispersions west of US 301. Shower and storm chances generally focus along the pinned Atlantic sea breeze late this afternoon but increase areawide Friday and into the weekend with a more active pattern emerging. This is partially due to potential tropical development in the northeast Gulf that we are currently monitoring.

Fog Potential and Other Remarks: Significant fog development is not expected for the next several nights. Gusty and erratic winds will be possible in and near thunderstorms, with occasional outflow boundaries capable of producing sudden wind shifts well away from ongoing convection.

PRELIMINARY POINT TEMPS/POPS

AMG 93 75 94 74 / 20 10 40 30 SSI 93 78 93 79 / 40 20 10 10 JAX 94 74 94 75 / 50 20 30 20 SGJ 93 78 93 75 / 50 10 30 10 GNV 94 75 93 73 / 40 30 60 50 OCF 95 75 92 74 / 60 30 70 60

JAX WATCHES/WARNINGS/ADVISORIES

FL...None. GA...None. MARINE...None.