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 through Next Week. Extreme Heat Warning Coastal Southeast GA Counties Today. Heat Advisory Elsewhere through 8 PM Today. Heat Advisory Saturday all local counties

- Scattered Strong and isolated severe thunderstorms this Afternoon and Evening, generally west of I-95. Storms Hazards: localized damaging wind gusts, frequent lightning strikes, blinding rainfall, and areas of flooding.

- Daily Scattered Afternoon thunderstorms through the next 7 days. Isolated severe thunderstorms for portions of Southeast GA possible on Saturday.

NEAR TERM /THROUGH TONIGHT/

Main Highlights:

- Extreme Heat Warning and Heat Advisories in Effect Rest of Today - Scattered Strong and isolated severe thunderstorms this Afternoon and Evening, generally west of I-95.

- Storms Hazards: localized damaging wind gusts, frequent lightning strikes, blinding rainfall, and areas of flooding.

A deeply moist and unstable airmass remains established. The morning upper air sampled 2.34" of precipitable water which well over the 90th percentile. This very moist setup will be able to tap into premium-grade instability aloft, with sample most- unstable CAPE also above the 90th percentile.

Dewpoints in the upper 70s with highs into middle 90s this afternoon will send the peak Heat Index values into the 105-112 range for most locations this afternoon. The hottest part of the day will be 2-6 PM today. Areawide heat advisory remains in effect through 8 PM this evening. The hottest areas are still expected along the SE GA coast where an Extreme Heat Warning is in effect until 8 PM as well.

Stacked ridging to the west will keep a weak westerly steering flow intact through the day upper-level easterly winds push anvils westward. Expect the initial convective development to focus along the Gulf and Atlantic sea breezes this afternoon, around 2 PM. The resulting outflow-sea breeze interactions will gradually shift scattered convection toward the US-301 where an early evening sea breeze merger will occur, generating numerous storms. With today's activity, a more pulse-like flavor of convection is expected. While most convection should stay below severe limits, given the degree of instability, a few isolated severe storms cannot be entirely ruled out this afternoon and evening. That means, precip-loaded downdrafts may produce gusty downbursts up to 50 mph despite the meager DCAPE along with frequent lightning and localized flooding.

After being worked over through the early evening, the loss of daytime heating should promote a downward trend and weakening in activity through 10 PM this evening. Given the amount of surface moisture, temperatures will be slow to cool off this evening and overnight, as lows fall back into the mid/upper 70s by daybreak on Saturday.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/

Main Highlights This Period:

- Isolated Strong to Severe Storms Saturday Afternoon/Evening

- Heat Index Values near or above Heat Advisory levels this weekend.

Dangerously hot temperatures continue this weekend, with the entire area Saturday under a Heat Advisory, and Sunday likely seeing Heat Advisory conditions as well (Heat Index 108-113 degrees). Some areas, especially near the southeast Georgia coast, will approach Extreme Heat Warning criteria, so the need to upgrade the Advisory to a Warning Saturday will be evaluated tonight. High temperatures both days will be in the mid to upper 90s, with mild lows in the mid to upper 70s.

Scattered to numerous showers and storms are forecast for Saturday, with highest chances generally I-10 northward where we will have higher PWATs. Enough surface instability, moisture, and higher DCAPE values will once again pose a damaging wind threat with any strong to potentially isolated severe thunderstorm development (focusing on southeast GA). The Storm Prediction Center has areas generally NW of Waycross under a Marginal severe risk, and the Weather Prediction has all of southeast Georgia under a Marginal Excessive Rainfall Outlook for Saturday. Overall, storm chances are lower on Sunday, in the 20-30% chance areawide.

LONG TERM /MONDAY THROUGH THURSDAY/

Main Highlights This Period:

- Hazardous Heat Continues into Next Week, with Daily Heat Advisories Possible

- Isolated to scattered thunderstorms each afternoon and evening, some which could become strong

Prolonged, hazardous heat continues Monday onward with high temperatures generally in the mid to upper 90s and afternoon heat index values reaching 106-113 degrees each day.

Early through mid-week, a front will be stalled across southern Georgia, which will limit storm coverage across southeast Georgia on Monday and Tuesday. The focus for convection will be across northeast Florida, as west/southwest surface winds bring the Gulf sea breeze far inland and the Atlantic sea breeze stays fairly close to the east coast. Wednesday through Friday, scattered afternoon and evening storms are expected each day area-wide.

AVIATION /18Z FRIDAY THROUGH 18Z SATURDAY/

Sea breezes will continue inland this afternoon, reaching the I-95 corridor around 20-21z. Early afternoon scattered thunderstorms will continue to develop amid a very unstable airmass. Periods of thunderstorms are likely at each airfield with highest confidence (60-80%) for NE FL airfields. The primary time frame with highest chances will be between 20-23z. Heavy downpours are likely to degrade visibility at times to IFR or LIFR. Outside of thunderstorm influence, VFR conditions persist. Overnight winds will trend light (< 5 knots or less) with mostly clear skies.

MARINE

A stagnant weather pattern, dominated by an upper ridge and reinforced surface trough to the north and surface high pressure extended across central and southern Florida. This will result in westerly, light offshore flow through the weekend and into next week. A southeast or south wind shift will occur across the near shore waters each afternoon as the sea breeze develops. The majority of thunderstorm activity will be inland but an isolated storm across the nearshore waters will be possible through the weekend.

Rip Currents: Generally low risk through the weekend with a prevailing offshore flow and low surf, around 2 feet. Low-end Moderate risk may develop during the afternoons as the sea breeze develops.

FIRE WEATHER

- Heat Headlines in Effect

Warm temperatures will continue through the end of the week, with highs in the mid 90s inland and lower to mid 90s along the coast today. Above-normal temperatures will persist through the weekend, with additional Heat Advisories likely, although isolated to scattered afternoon and evening thunderstorms may provide some relief and limit the duration of heat index values near or above advisory criteria. A cold front will move south into the area Saturday and stall near the Florida/Georgia line Sunday, focusing the highest storm chances along and south of the boundary, particularly toward the I-10 corridor Saturday. Dispersion looks to be good through the weekend.

Fog Potential: Significant fog development is not expected. Any late- night or early-morning fog should be shallow and patchy, mainly in areas that receive locally heavy rainfall.

PRELIMINARY POINT TEMPS/POPS

AMG 97 75 96 76 / 50 20 50 10 SSI 95 79 95 80 / 50 10 50 10 JAX 95 76 96 77 / 50 20 60 10 SGJ 94 77 95 77 / 40 10 30 10 GNV 95 74 95 75 / 60 30 30 10 OCF 96 75 96 75 / 50 30 20 10

JAX WATCHES/WARNINGS/ADVISORIES

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