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 to Numerous Afternoon & Early Evening Thunderstorms along the I-95 and U.S. Highway 17 Corridors. Strong to Isolated Severe T'Storms are Possible, with Wind Gusts of 40-60 mph, Frequent Lightning Strikes, and Heavy Downpours.

- Squall Line of Strong to Isolated Severe Thunderstorms May Traverse Inland Portions of Southeast GA Overnight through the Predawn Hours on Friday. Wind Gusts of 40-60 mph, Frequent Lightning Strikes, and Heavy Downpours will be Possible.

- Numerous Showers and Thunderstorms Expected on Friday and Saturday. Strong to Isolated Severe Storms Will be Possible.

- Heat Index Values Increasing to Near Heat Advisory Levels Early Next Week.

- KVAX (Valdosta, GA) Radar is Out of Service. Please utilize other area radars for active weather this afternoon and tonight.

NEAR TERM /THROUGH TONIGHT/

Main Highlights Today and Tonight:

- Scattered to Numerous Afternoon & Early Evening Thunderstorms Along the I-95 and U.S. Highway 17 Corridors. Strong to Isolated Severe T'Storms are Possible, with Wind Gusts of 40-60 mph, Frequent Lightning Strikes, and Heavy Downpours.

- Squall Line of Strong to Isolated Severe Thunderstorms May Traverse Inland Portions of Southeast GA Overnight through the Predawn Hours on Friday. Wind Gusts of 40-60 mph, Frequent Lightning Strikes, and Heavy Downpours will be Possible.

Afternoon surface analysis depicts remnant low pressure (1007 millibars) from former Tropical Storm Arthur traversing the lower Mississippi Valley, with this feature beginning to accelerate northeastward and creating an expanding region of heavy downpours and strong to severe storms across the Deep South. Meanwhile, a cold front extends from the eastern Great Lakes through the Ohio Valley and the Ozarks. Aloft...troughing that was progressing slowly across southeastern Canada and the Great Lakes has displaced deep-layered ridging to the east of the Bahamas, creating a deepening southwesterly flow pattern across our area. Latest GOES-East derived Total Precipitable Water imagery indicates that deep tropical moisture remains in place over our area, with PWATs generally in the 1.8 - 2 inch range, with a slightly drier air mass over the northeast Gulf, featuring PWATs around or just below 1.75 inches poised to move onshore along the FL Big Bend and Nature Coast later today. A hot and unstable airmass in place across our region was aiding in the development of widely scattered showers and thunderstorms, with activity across southeast GA moving briskly northeastward, while lighter steering flow was resulting in slower moving convection over north central FL. Outside of rain cooled locations, temperatures at 19Z were in the low to mid 90s, with dewpoints in the 70s, creating heat index values of 100-105 at most locations.

Scattered convection should continue to blossom in the warm and unstable air mass that is in place across inland locations, with relatively fast storm motion expected. This environment should allow convection to pulse and become strong, with isolated severe storms possible. Otherwise, the Atlantic sea breeze boundary has formed at coastal locations, and this boundary will likely serve as another focus for strong to isolated severe thunderstorms through the late afternoon and early evening hours. Surface based CAPE values in excess of 2,000 j/kg and gradually strengthening southwesterly speed shear should allow for a few storms to pulse this afternoon before moving offshore this evening, with stronger storms capable of producing downburst winds of 40-60 mph, along with frequent lightning strikes and torrential downpours. Faster storm motion should preclude flood concerns at most locations, although some threat for training cells may develop at coastal locations based on strengthening, mostly unidirectional flow. Activity should then move offshore after midnight tonight.

Low pressure is expected to accelerate northeastward across AL and GA tonight, with a trailing band of convection likely approaching the Ocmulgee / Altamaha Rivers towards midnight. This storm system will bring a 40-45 knot southwesterly low level jet around 850 millibars (around 5,000 feet) across inland portions of southeast GA tonight, which could maintain a broken squall line containing strong to severe storms into the overnight and predawn hours. CAMs have been wavering on whether this activity will ultimately weaken as it moves into southeast GA after midnight, but the Storm Prediction Center has maintained a "Marginal" (level 1 out of 5) risk for isolated severe storm potential, and enough low level veering may still be in place for isolated tornado potential, mainly for locations north and west of Waycross. A southwesterly breeze overnight will otherwise keep lows in the 75-80 degree range across our area.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/

- Isolated Strong to Severe T'storms Friday. - Numerous to Widespread Showers and T'storms Saturday.

- Hot and Humid Conditions Friday into Saturday.

Pattern for daily bouts of showers and storms will continue through Friday and Saturday as the moist southwesterly flow pattern persists over the forecast area between the frontal boundary to the north and an area of high pressure rotation east of the Florida peninsula over the Gulf. Scattered to numerous are expected through this period with a potential for strong storms on Friday capable of producing destructive winds, frequent lightning, and a potential for localized flooding with training storms as PWAT values measure upwards of 2.4 inches over the region. High temperatures for the end of the week and into the weekend will rise into the upper 80s and lower to mid 90s with overnight low temperatures dropping down into the lower to mid 70s over inland areas and in the mid to upper 70s along the coastline. Heat index values rise to values of over 100 Fahrenheit with conditions rising to be near Heat Advisory levels over portions of southeast Georgia and northeast Florida.

LONG TERM /SUNDAY THROUGH THURSDAY/

Main Highlights This Period:

- Heat index values increasing to near Heat Advisory levels next week.

- Decreasing chances for showers Afternoon and Evening T'storms Sunday through next week.

Drier air will filter in over the region by end of Sunday and into Monday as drier air associated a high pressure system over the Gulf extends in over the forecast area resulting in more inhibited convection for the beginning of next week, with the prevailing flow shifting about to become more out of the west and northwest. Temperatures will warm through the weekend and into next week with max temps rising into the mid to upper 90s before midweek. Heat index values are expected to rise to be 100 and higher for portions of southeast Georgia and northeast Florida, with a potential for a return to Heat Advisory level conditions next week.

AVIATION /18Z THURSDAY THROUGH 18Z FRIDAY/

VFR conditions will prevail through at least 20Z at the regional terminals. Showers and thunderstorms will continue to increase in coverage and intensity across our region later this afternoon, with confidence remaining high enough to maintain at TEMPO group at SGJ through 01Z for potential wind gusts up to 30 knots and IFR visibilities during heavier downpours. Confidence has increased enough to also include TEMPO groups at CRG and SSI during this time frame for similar conditions. PROB30 groups were maintained at JAX and VQQ around 20Z-01Z for brief wind gusts up to 30 knots and MVFR visibilities during heavier downpours. We have maintained only vicinity shower coverage at GNV for now. Scattered thunderstorms that develop along the I-95 corridor late this afternoon will move offshore before 02Z this evening, with another round of thunderstorms expected to impact inland portions of southeast GA towards 06Z Friday. Confidence remains too low to include anything other than vicinity shower coverage at SSI and the Duval County terminals overnight through early Friday morning. Showers and thunderstorms will likely increase in coverage towards the end of this TAF period, or during the early afternoon hours on Friday. South-southwesterly surface winds will remain sustained at 10-15 knots and gusty outside of thunderstorm activity at the inland terminals through around 00Z. The Atlantic sea breeze boundary will move slowly inland this afternoon, shifting surface winds to southeasterly at SGJ and southerly at SSI at 10-15 knots towards 20Z. Southerly surface winds will remain somewhat elevated overnight, with sustained speeds generally remaining around 10 knots. Surface winds will then shift to southwesterly after sunrise, with speeds increasing to around 15 knots by 16Z.

MARINE

Low pressure moving across the southeastern states this afternoon and tonight will result in strengthening southwesterly winds, with Caution conditions expected throughout our local waters tonight. Winds may briefly approach Small Craft Advisory levels across the Georgia waters overnight through Friday morning. Otherwise, strong to isolated severe thunderstorms developing near coastal locations could impact much of our local waters during the early evening hours, with stronger storms being capable of producing strong wind gusts, frequent lightning strikes, and torrential downpours. Activity should move eastward over the Gulf Stream waters by midnight, with another round of storms potentially approaching the Georgia waters during the predawn hours on Friday from the northwest.

Low pressure will then accelerate east-northeastward across the Carolinas on Friday, emerging off the Outer Banks towards sunset. A frontal boundary trailing this departing low pressure center is expected to stall just north of the Georgia waters on Friday and Saturday. Additional rounds of strong to possibly severe thunderstorms will potentially impact our waters from Friday through the weekend as a prevailing west winds continue. Coverage of showers and thunderstorms may decrease slightly early next week ahead of another frontal boundary that will likely stall across the southeastern states by midweek.

Rip Currents:

Breezy southerly winds developing in the wake of the inland moving Atlantic sea breeze may create a lower end moderate risk for the northeast FL beaches. Low surf heights should keep the risk low at the southeast GA beaches during the next several days. Similar conditions will prevail on Friday, with a lower end moderate risk possibly developing during the afternoon at the northeast FL beaches. Light offshore winds this weekend will likely result in a low risk at all area beaches, and strengthening offshore winds early next week should keep surf heights low enough to maintain a low risk.

FIRE WEATHER

- Patchy High Dispersion Values Today and Friday.

Moist and unstable airmass will continue afternoon/early evening scattered to numerous T'storms today as west to southwest winds allow the Gulf seabreeze to move quickly eastward to the Atlantic coast before interacting with the pinned Atlantic seabreeze near the Atlantic coast. T'storms will include heavy downpours and locally heavy rainfall, frequent lightning, and gusty winds with isolated strong to severe T'storms this afternoon. A front will sink towards the area Friday and move through Northeast Florida Saturday with widespread showers and T'storms. The front will stall near north central or central Florida Sunday with less coverage of T'storms.

Favorable transport winds and mixing heights will lead to areas of high afternoon dispersion values today along and west of I-95. Good level dispersions expected during each afternoon Friday into the weekend as more clouds limit mixing heights while transport winds decrease slightly as the front settles south of the area by Sunday.

Temperatures will be hot today and along with elevated humidity will create heat index values up to 102-106 near the coast and across Northeast FL. Highs will decrease to the low 90s Friday into the weekend, but high humidity levels will continue.

FOG POTENTIAL AND OTHER REMARKS: Areas that receive heavier rainfall may also experience patchy late-night and early-morning fog.

EQUIPMENT

The WSR-88D Radar located near the Moody AFB near Valdosta remains offline due to technical problems. Technicians are awaiting critical parts to restore functionality. During the outage please utilize other area radars...KJAX, KTLH, or KJGX.

PRELIMINARY POINT TEMPS/POPS

AMG 74 85 73 88 / 80 60 40 70 SSI 78 91 77 89 / 50 70 30 70 JAX 78 92 76 90 / 30 60 50 90 SGJ 77 94 77 91 / 40 40 30 90 GNV 78 92 76 91 / 10 50 40 90 OCF 78 92 77 91 / 20 40 40 80

JAX WATCHES/WARNINGS/ADVISORIES

FL...Heat Advisory until 7 PM EDT this evening for FLZ023-024-030- 031-038-124-125-132-136>138-140-225-232-233-236-237-240- 325-333-340-425-433-533-633. GA...Heat Advisory until 7 PM EDT this evening for GAZ152>154-165- 166-264-350-364. MARINE...None.