Area Forecast Discussion

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 Showers & Thunderstorms through Early this Evening. Isolated Strong Thunderstorms Possible, Mainly for Locations West of U.S.-301. Hazards: Gusty Winds 40-50 mph and Localized Flooding. Limited Storm Coverage Wednesday to Friday

- Seasonably Hot Conditions Continue Peak Heat Indices 102-108

- Moderate Rip Current Risk through Wednesday, lower risk Thursday

- Small Craft Advisories through Tonight Across our Local Atlantic Waters

NEAR TERM /UNTIL 8 AM WEDNESDAY MORNING/

The region will be between high pressure to the east, and tropical storm Bertha to the west Tonight. Convection will continue to dissipate this evening, with a dry overnight. Lows Tonight in the middle 70s will be common.

SHORT TERM /8 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/

Main Highlights This Period:

- Unseasonably Dry Weather Expected on Wednesday.

- Isolated to Widely Scattered Thunderstorms return Thursday Afternoon and Evening at Inland Locations.

- Seasonably Hot and Humid Weather Continues, with Breezy Conditions Persisting on Wednesday.

Stout ridging aloft centered over the Southern Plains will continue to extend its axis east-southeastward into the southeastern states through Thursday night. Meanwhile, a potent shortwave trough pivoting across the eastern Great Lakes and southeastern Canada will drive a frontal boundary southward across the Tennessee Valley and the southern Appalachians, with this boundary then stalling to the north of our area by Thursday evening. Ridging aloft will continue to direct Tropical Storm Bertha westward towards coastal Louisiana, with a drier and more subsident air mass overspreading most of our area from east to west on Wednesday. A late day surge of slightly deeper moisture over the FL peninsula moving northward could develop a few thunderstorms across north central FL on Wednesday evening, but an unseasonably dry afternoon and evening is otherwise forecast for the rest of our area. Highs will soar to the mid and upper 90s at inland locations and the low to mid 90s at coastal areas, with the drier and more subsident air mass allowing dewpoints to mix down to the upper 60s at most inland locations, keeping peak Heat Index values just below Heat Advisory criteria. Breezy onshore winds developing in the wake of the inland moving Atlantic sea breeze could push Heat Index values closer to the 108 degree Heat Advisory threshold at coastal locations as dewpoints rise to the mid and upper 70s late on Wednesday afternoon.

Any isolated convection that develops over north central FL on Wednesday afternoon or evening should dissipate before midnight, with fair skies and gradually diminishing south or southwesterly winds keeping inland lows in the mid 70s, with upper 70s to around 80 forecast at coastal locations.

Model soundings still indicate that PWATs will remain slightly below late July climatology across most of our area on Thursday. There should be just enough moisture for isolated to widely scattered mainly late afternoon and evening convection to develop for locations along and west of U.S. Highway 301 as mesoscale boundaries moving well inland collide. The overall subsident air mass should keep thunderstorms that manage to develop rather tame and likely short lived, with dry conditions expected to continue at coastal locations. Highs on Thursday will generally climb to the mid and upper 90s inland, while an earlier developing sea breeze keeps coastal highs mostly in the lower 90s. Dewpoints will again likely mix down to the upper 60s and lower 70s inland, keeping heat index values just below Heat Advisory criteria, with coastal locations more likely to approach this criteria as dewpoints rise to the mid and upper 70s.

Convection should again conclude before midnight on Thursday night, with lows at inland locations mostly falling to the mid 70s, with coastal locations again forecast to remain in the upper 70s to around 80.

LONG TERM /FRIDAY THROUGH TUESDAY/

Main Highlights This Period:

- Scattered to Numerous Afternoon Thunderstorms, Especially Friday into the Weekend.

- Increasing Chances for Afternoon and Evening Thunderstorms Late this Weekend and Early Next Week.

- Potential Heat Advisory Conditions this Weekend and Early Next Week.

Stout ridging aloft centered over the Southern Plains states will retrograde to the Four Corners region of the Desert Southwest from Friday through the weekend. This will allow troughing to dig into the southeastern states by late in the weekend and early next week. An extension of the ridge centered well to the west of our area will remain in place across the Deep South on Friday and Saturday, likely keeping a more subsident air mass in place locally, especially on Friday. Model blends currently indicate only isolated afternoon convective potential across inland portions of southeast GA on Friday, with isolated to widely scattered afternoon and evening thunderstorms returning on Saturday. Highs on Friday and Saturday will again soar to the mid and upper 90s inland and the low to mid 90s at coastal locations. The more subsident air mass should again allow dewpoints to mix down to the upper 60s and lower 70s at inland locations on Friday at inland locations, keeping peak heat indices mostly in the 100-108 degree range. Heat index values could reach Advisory levels across portions of northeast and north central FL on Saturday afternoon. Lows will only fall to the mid and upper 70s at most locations.

Moisture will deepen from north to south from Sunday through the early portion of next week as troughing digs into our area. This should activate scattered to possibly numerous afternoon and evening thunderstorms, mainly along mesoscale boundaries as west to southwesterly low level flow deepens downstream of a stalled frontal boundary. A few stronger storms will be possible on Sunday and Monday afternoons along the I-95 corridor as convection potentially interacts with a pinned Atlantic sea breeze boundary. Highs on Sunday may remain in the low to mid 90s, with increasing humidity values likely bringing heat index values close to Heat Advisory criteria. Ridging aloft will then begin to expand into the southeastern states early next week, potentially raising highs to the mid to upper 90s, especially for inland locations north of the I- 10 corridor. Lows will generally remain in the mid and upper 70s across our region this weekend and early next week.

AVIATION /00Z WEDNESDAY THROUGH 00Z THURSDAY/

Remaining convection will dissipate early this period. Prevailing VFR conditions forecast for the overnight, and through the day Tuesday. While chances for convection are not zero Tuesday, the chances are much lower than average.

MARINE

Breezy southerly winds between the Tropical Storm Bertha and the Bermuda high will lead a couple more days of breezy conditions. Winds will increase to Small Craft Advisory levels this afternoon and remain elevated through early Wednesday. Seas will rise toward 5 or possibly 6 feet today in response to the winds. Relaxing winds are expected Wednesday night as flow generally trends offshore as a weak cold front approaches from the northwest. The front is likely to stalls north of the waters this weekend as waves of low pressure track along it. Though offshore flow will be in place from Thursday onward, afternoon winds in nearshore waters will be driven by the coastal sea breeze development each afternoon.

Rip Currents:

Increasing southerly winds along with sea breeze development will push elevated wind waves into the coastline this afternoon along with strong longshore. Given a minimal onshore swell, the rip current risk will be on the upper-end of Moderate this afternoon but not quite High Risk. Moderate risk is likely again Wednesday before falling Thursday.

FIRE WEATHER

- High Daytime Dispersion Values Inland Through Wednesday

Scattered thunderstorms will be possible through early this evening, mainly for locations west of the U.S. Highway 301 corridor in southeast GA, the Suwannee Valley, and north central FL. Only isolated to widely scattered afternoon and early evening thunderstorms are forecast from Wednesday through Saturday. Otherwise, breezy southerly transport winds will continue through Wednesday, creating high daytime dispersion values at inland locations. Surface winds will become southeasterly during the afternoon hours at coastal locations, where fair to good daytime dispersion values are forecast. Transport winds will then gradually weaken on Thursday and Friday, with south-southwesterly winds prevailing on Thursday and then a light westerly wind pattern developing by Friday. Elevated mixing heights will generally yield good daytime dispersion values inland, with fair values forecast at coastal locations, where breezy onshore surface winds will develop early on Thursday and Friday afternoon.

Fog Potential and Other Remarks: Significant fog development is not expected during the next several nights.

PRELIMINARY POINT TEMPS/POPS

JAX WATCHES / WARNINGS / ADVISORIES

FL...None. GA...None. MARINE...Small Craft Advisory until 5 AM EDT Wednesday for AMZ450-452- 454-470-472-474.