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 & Evening TStorms Each Day. Heavy Rainfall Potential Today & Friday for Northeast & North Central FL. Localized Flash Flooding Possible, Especially at Urban Locations. Heavy Downpours Possible Area-Wide on Sunday and Monday Afternoons

- Heat Advisory Conditions Possible on Friday Afternoon. Peak Heat Index Values of 105-110 Possible

UPDATE

No major updates this evening, a few showers will approach the SE GA coast through midnight, with coastal showers redeveloping offshore after midnight, then shifting onshore a little after sunrise. Patchy fog will develop after midnight inland across SE GA and portions of the Suwannee Valley along and north of I-10, but not expecting dense fog as past couple of mornings due to cloud cover. Lows will be in the mid 70s inland and upper 70s to near 80 at the coast.

NEAR TERM /THROUGH FRIDAY/

Highlights Today and Tonight:

- Waves of showers and embedded thunderstorms with heavy rainfall and gusty winds today and tonight, mainly across Northeast Florida

- High Risk of rip currents at Northeast Florida beaches

This morning's sounding as well as GOES Precipitable Water Analysis show deep tropical moisture across the area, with PWATs near 2-2.3". Today is our final day of strong onshore flow before a weather pattern shift. Showers will continue to move inland off the Atlantic through the afternoon, with convective coverage increasing this afternoon and evening mainly for inland northeast Florida. The primary weather concern today will be heavy downpours posing a localized flooding threat. Conditions are not overly favorable for strong thunderstorms today as heavy cloud cover limits instability, but a few strong storms near I-75 can't be ruled out, with gusty winds being the main hazard from those. The persistent onshore breeze and morning showers will keep coastal highs in the mid to upper 80s, with inland highs reaching the low 90s.

Similar to this morning, there will be a patchy fog and low stratus risk for Friday morning for most inland locations, as well as early morning showers near the coast.

SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/

Main Highlights This Period:

- Strong Storm Potential at Inland Locations on Friday Afternoon and Evening.

- Heavy Downpours at Inland Locations Will Increase the Threat for Localized Flooding, Especially at Urban Location

- Strong Storm Potential Shifts to the I-95 Corridor on Saturday Afternoon and Evening

Ridging aloft will remain in place over the southeastern states on Friday, with Atlantic surface high pressure anchored just off the southeastern seaboard. Meanwhile, a Tropical Upper Tropospheric Trough (TUTT) will get steered slowly northwestward towards the central Gulf coast, which will veer our low and mid level flow from southeasterly on Friday morning to southerly by Friday afternoon. This flow will advect deep tropical moisture that is currently in place across north central and northeast FL (PWATs of 2.25 to 2.5 inches) northward across southeast GA by Friday afternoon. Southeasterly low level flow will keep the potential for morning showers and a few embedded thunderstorms along the I-95 corridor, mainly across southeast GA, with activity potentially shifting well inland after sunrise. Low clouds and possibly some locally dense fog developing around sunrise at inland locations in southeast GA should lift by the mid-morning hours, with morning convection likely lifting north of the Altamaha River towards noon. This will set the stage for a seasonably hot and humid day across our area, with heat index values soaring to the 100-108 degree range by the early to mid afternoon hours. Highs will generally climb to the low and mid 90s, except upper 80s at coastal locations, where onshore winds will prevail throughout the day.

Abundant tropical moisture and a more southerly steering flow will allow for scattered thunderstorms to develop along the inland moving Gulf coast sea breeze boundary, with activity likely increasing in coverage and intensity during the mid to late afternoon hours as mesoscale boundary collisions tend to focus near the U.S. Highway 301 corridor. Convection should also shift northward into southeast GA by the late afternoon hours, with activity then potentially getting steered eastward towards the I-95 corridor during the early evening hours. Colliding mesoscale boundaries could cause a few storms to "pulse" and become strong, with downburst wind potential of 40-50 mph, along with frequent lightning strikes and torrential downpours. Weakening steering flow should allow for slower storm motion, which may increase the threat for localized flooding, especially at urban and normally flood prone locations.

Activity will generally weaken and dissipate during the mid to late afternoon hours across inland southeast GA and along the I-95 corridor, with debris cloud cover thinning out after midnight. Atlantic ridging will shift southward on Friday night, allowing for continued veering of our low level wind field. A south-southwesterly flow pattern should develop predawn and early morning convection along the FL Big Bend and Nature Coasts, with this activity potentially shifting inland over the Suwannee Valley and north central FL, generally for areas west of I-75. Lows on Friday night will generally fall to the low and mid 70s inland and the mid to upper 70s at coastal locations.

Troughing digging southward across New England and the Mid-Atlantic states on Saturday will allow the "Heat Wave" ridge over the southeastern states on Friday to retrograde westward towards the Plains states. This shift in the weather pattern will allow for a cold front to shift southward through the Carolinas, and the Atlantic ridge axis will also shift southward, creating a deepening southwesterly wind flow across our area. This will bring heat and humidity to expand to coastal locations, as the development of the Atlantic sea breeze boundary will be delayed until the early to mid afternoon hours. Highs will again soar to the low and mid 90s, with heat index values potentially approaching Heat Advisory criteria (108 degrees) before widespread convection erupts along inland moving sea breeze boundaries, mainly during the early to mid afternoon hours. The Gulf sea breeze boundary will likely be dominant in terms of convective coverage, with a sea breeze collision likely along the I-95 corridor during the late afternoon hours, where strong storms are possible as mesoscale boundaries collide and storms "pulse". Steering flow may remain weak enough for slow moving downpours, especially for locations east of I-75, and localized flooding will be possible, especially at urban and normally flood prone locations.

Activity should shift northeastward into southeast GA by the late afternoon hours, with convection then moving offshore of coastal northeast FL early in the evening. Another round of nocturnal and predawn convection can be expected over the northeast Gulf, with this activity potentially moving onshore and shifting towards I-75 towards sunrise on Sunday. Debris cloud cover will otherwise thin out during the overnight and predawn hours, with lows mostly falling to the low and mid 70s.

LONG TERM /SUNDAY THROUGH THURSDAY/

Main Highlights This Period:

- Numerous Afternoon and Evening Thunderstorms Expected on Sunday. Strong Storm Potential Continues Along the I-95 Corridor.

- Afternoon and Evening Thunderstorm Coverage Shifts Inland Early Next Week.

- Breezy Onshore Winds Expected During the Early to Middle Portions of Next Week

Troughing aloft will continue to dig over the eastern third of the nation on Sunday and Monday, shifting a cold front southward into southeast GA by Sunday afternoon. This front will begin to slow its forward progress as it nears the Interstate 10 corridor on Monday as surface high pressure begins to wedge down the southeastern seaboard. Troughing will then shift away from our region towards the middle portion of next week, allowing for ridging to begin to expand into the southeastern states.

Deep-layered westerly flow and tropical moisture pooling ahead of the approaching frontal boundary will develop widespread mainly afternoon and evening thunderstorms on Sunday. Seasonably hot and humid weather will feed the potential for strong storms, especially where mesoscale boundaries collide, which should be along the I-95 corridor during the mid to late afternoon hours. Highs will again soar to the low and mid 90s, with heat index values potentially approaching Heat Advisory criteria during the early to mid afternoon.

The presence of troughing aloft and the frontal boundary sagging into our area may keep convection going on Sunday evening, especially across southeast GA. Low and mid level flow will then shift to east-northeasterly on Labor Day as surface high pressure wedges down the southeastern seaboard during the afternoon hours. This shift in the weather pattern should focus strong storm potential over inland locations on Monday, with widespread heavy downpours keeping the threat for localized flooding in place. This onshore wind regime and the slowing frontal boundary should keep highs in the upper 80s and lower 90s during the early to middle portions of next week. A tightening local pressure gradient will create breezy conditions at coastal locations, where highs may be held to the mid 80s. Nighttime convection may continue on Monday night for locations south of I-10, with convection then becoming more diurnal in nature by Tuesday and next Wednesday as the frontal boundary washes out.

AVIATION /00Z FRIDAY THROUGH 00Z SATURDAY/

The 00Z TAF period will begin with mainly VFR conditions with periodic MVFR ceilings at SSI in the moist onshore flow through 04Z. Light easterly winds 5 to 8 knots will become light and variable inland by 04Z-06Z with IFR ceilings and MVFR fog developing after 06Z through 14Z. The ceilings will lift to MVFR levels near 2.5 kft by 14Z. VFR ceilings will return by 17-18Z as ceilings become scattered 2.5-3.0 kft at all TAF sites.

High pressure will shift more to the east northeast while an upper wave moves off to the west northwest which will shift the winds to southerly, increasing to 6-8 knots from the south, then become southeasterly behind the Atlantic seabreeze around 10-12 knots under mid level clouds while GNV winds remain southerly under 10 knots.

A slug of low and mid level moisture will lift north from NE FL into SE GA with gradually increasing showers lifting north across the area late Friday morning into early afternoon with scattered to numerous showers and thunderstorms in the afternoon hours as the Atlantic seabreeze moves from the coast to CRG/JAX/VQQ as strong heating, storm outflow and the seabreeze interactions increase coverage. A stronger thunderstorm may impact the terminals in the afternoon, so have noted a PROB30 group for all Northeast Florida TAF sites after 17-19Z with IFR visibility and MVFR ceilings along with gusty winds up to 25 knots. Storms will diminish in coverage at the end of the period.

MARINE

Onshore east to southeast flow will continue waves of showers and embedded thunderstorms at times through Friday. Prevailing westerly winds are then expected from Saturday through at least Monday morning as a frontal boundary sinks southward towards our region, with this feature maintaining a stormy weather pattern. Stronger high pressure will build down the southeastern seaboard early next week in the wake of this boundary, likely pushing the front over the northeast Florida waters.

Rip Currents: A long period east-southeasterly ocean swell will combine with breezy northeasterly winds to create breakers of 3-4 feet at the northeast FL beaches and 2-3 feet at the southeast GA beaches Today. These conditions will yield a high risk of deadly rip currents at the northeast FL beaches and a higher end moderate risk for the southeast GA beaches. The long period swell will gradually fade tonight and should not linger into Friday, with the afternoon sea breeze creating enough of an onshore breeze to yield a lower end moderate risk on Friday at area beaches. Prevailing offshore winds this weekend should result in a low risk, while developing onshore winds on Labor Day likely resulting in at least a moderate risk.

FIRE WEATHER

Widespread afternoon and evening showers and thunderstorms are forecast from Friday through Tuesday throughout our region. Strong storms potential will focus over inland locations on Friday afternoon through early evening, followed by stronger storm potential shifting to the Interstate 95 corridor during the afternoon and early evening hours on Saturday and Sunday. Stronger storm potential will then shift back to inland locations during the afternoon and early evening hours on Labor Day. Stronger storms will be capable of producing strong surface wind gusts, frequent lightning strikes, and torrential downpours. Southeasterly surface and transport winds will prevail on Friday, followed by winds shifting to southwesterly on Saturday and westerly on Sunday. Poor to fair daytime dispersion values will continue each day, with pockets of good values possible at inland locations on Sunday. Otherwise, seasonably hot and humid weather is forecast area-wide, with peak heat index values generally around 105 degrees each afternoon before thunderstorm coverage increases.

Fog Potential: Gusty and erratic winds can be expected in and near thunderstorms with briefly localized flooding rainfall. Late night and early morning fog and low cloud cover will be possible on Friday and Saturday mornings at inland locations, with locally dense fog possible early on Friday morning across interior portions of southeast Georgia.

PRELIMINARY POINT TEMPS/POPS

AMG 74 91 73 92 / 10 70 10 40 SSI 78 88 77 90 / 20 50 10 50 JAX 75 90 74 92 / 10 70 10 60 SGJ 76 89 75 91 / 20 60 20 60 GNV 74 91 73 91 / 10 70 20 60 OCF 74 91 74 91 / 20 80 20 60

JAX WATCHES/WARNINGS/ADVISORIES

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