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 Thunderstorms Hazards: Wind Gusts of 35-45 mph, Frequent Lightning & Localized Flooding

- Heavy Rainfall & Localized Flooding Possible on Sunday and Monday with Increasing Thunderstorm Coverage, mainly NE and North Central FL

- Moderate Rip Current Risk at area beaches this afternoon

- Heat Advisory Conditions Possible Towards the Middle of Next Week

NEAR TERM /THROUGH TONIGHT/

Main Highlights Today and Tonight:

- Seasonably Hot and Humid Summertime Weather Continues.

- Strong Pulse Thunderstorms possible late this afternoon for inland NE FL, mainly along the I-75 corridor; Localized Urban Flooding possible.

For today...Convection will be more abundant this afternoon, particularly across NE FL owing to the lift and destabilization offered by a developing upper low. With weak steering flow, convective evolution will follow typical summer trend with the Gulf and Atlantic sea breezes moving inland, colliding along the US 301 corridor this afternoon. Before the potential relief from afternoon storms, highs will push toward the mid 90s inland and make it to around 90 at the coast before the sea breeze moves onshore. Peak heat index will be seasonably hot but not likely to reach Heat Advisory criteria this afternoon.

As mentioned above, a tropical upper tropospheric trough lifting across south Florida this morning will gradually move northwestward and close off into an upper low over the northeastern Gulf this afternoon. As it does so, a cold pool of air in the mid levels will begin to push into north central FL this afternoon helping to steepen mid level lapse rates over those zones. Deep easterly flow strengthening around the northeastern periphery of the upper low will bring in some drier air which may cap convection somewhat initially along the sea breeze. The potential for stronger convection and potential for gusty winds, downpours, and frequent lightning episodes will generally favor areas west of the St Johns River and south of I-10 where the steeper lapse rates and forcing will overlap colliding sea breeze and outflow boundaries during the late afternoon and early evening hours (5-9 PM).

Due to the high-grade - above the 90th percentile - precipitable water (2.25"+), a localized heavy rain and urban flash flooding is a potential concern this evening for areas along I-75 from Lake City southward. The latest HiRes Ensemble CAMs have identified a medium (30-50%) probability of the aforementioned areas to accumulate 3" or more rain over a 3 hour period which is a more "aggressive" amount but worth mentioning.

Otherwise, convection will exit to the west during the late evening hours with skies clearing behind it. Due to heavy rain, there is potential for some patchy fog along the Suwannee River valley during the early hours Saturday.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/

Main Highlights:

- Heavy Rain and Localized Flood Concerns - Daily bouts of showers and storms

A Tropical Upper Tropospheric Trough (TUTT) will be located along the west FL coast Saturday with an embedded upper low located near Tampa. This upper low pressure center will slowly migrate north- northeast through Sunday, but become more ill-defined into early next week. Model guidance also shows quasi-stationary surface troughing extending from the central Carolinas to the FL panhandle into the eastern Gulf. A weak surface low may attempt to develop beneath the upper feature and acquire some subtropical or tropical characteristics as it moves northeast on Sunday. However, confidence in surface low development remains low, with the National Hurricane Center maintaining a 20 percent chance of tropical development.

The combination of the rich moisture with PWATs around 2 inches and temperatures cooling aloft will increase afternoon and evening thunderstorm coverage. Deep layer flow is southerly both days about 10 mph, perhaps a little stronger on Sunday.

Regardless of tropical development, the deep tropical airmass will overspread the region through the weekend, supporting numerous showers and thunderstorms each afternoon and evening. Best convective coverage and heavy rainfall amounts look to occur over inland areas generally south of Waycross for both days, as the east coast sea breeze should push inland far enough to keep the bulk of the heavier storms further west. The primary hazard with storms will be periods of heavy rainfall capable of producing localized flooding, especially across northeast and north central Florida where repeated rounds of convection are most likely. Frequent lightning and locally gusty winds will accompany the stronger storms.

Temperatures will remain seasonably hot Saturday, with highs in the lower to middle 90s and peak heat index values of 102 to 107 degrees. Increasing cloud cover and numerous showers and storms on Sunday should hold highs closer to the upper 80s to lower 90s while maintaining humid conditions.

LONG TERM /MONDAY THROUGH THURSDAY/

Main Highlights For Next Week:

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

Weak mid to upper level trough will continue across the region early next week, oriented from the eastern Gulf then northeastward over our forecast area to the Carolina coast. This upper trough looks to weaken and become less defined by mid week. Low level troughing also continues over the southeast states into the northeast Gulf early next week. Importantly, the northeast Gulf continues to be an area that is being monitored by the NHC early next week with low chances of tropical development. Still much uncertainty if anything develops given it would be close to land and models are having a hard time showing anything well-defined. As low to mid level ridging begins to build back in over the FL peninsula by Wednesday, any troughing or low pressure would shift northward. Still looks like numerous showers and storms for Monday and Tuesday, especially over northeast and north central FL. The high PWAT air of near 2 to 2.2 inches (near or above the 90th climate percentile), coupled with convergent south or southwest low level flow will support a localized flooding rain threat for inland areas, especially northeast and north central FL.

Coverage of convection appears to decrease slightly Wednesday and Thursday. At the same time, increasing heights aloft will allow temperatures to climb back into the middle 90s, with oppressive humidity pushing peak heat index values to about the 105 to 110 degree range by midweek. Given this, heat advisory conditions may become increasingly likely for some areas.

AVIATION /06Z FRIDAY THROUGH 06Z SATURDAY/

VFR conditions through 17z, though a one to two hour period of low- based cumulus (around 2kft) will be possible around 15z. Sea breeze activity will push inland faster this afternoon, limiting the potential for convective impacts at KSSI, KSGJ, and KCRG as well. Main areas and terminals impacted by TSRA will be west of I-95 with increasing chances the farther west you go. Heavy rain with thunderstorms will restrict terminal visibility to IFR or less temporarily. The concentration of convection will be along the Gulf and Atlantic sea breeze merger, which will be near KGNV around 20- 22z. Expect Atlantic sea breeze to arrive around 16z at coastal terminals then KJAX/KVQQ around 18z/19z.

MARINE

Light flow will favor a dominant sea breeze wind pattern this afternoon. This weekend southerly winds will strengthening to Exercise Caution levels as gradients increase between a trough over the southeastern US and strengthen Bermuda high pressure. As steering flow pattern turns offshore this weekend, chances for afternoon thunderstorms will increase.

Surface troughing will strengthen 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 disturbance development. The weak wave of low pressure should progress northeastward across our local waters early next week.

Rip Currents:

Sea breeze winds this afternoon will lead to a low-end moderate risk of rip currents this afternoon. 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

Surface and transport wind speeds are forecast to be weak today which will lead to poor to fair dispersion values. Slightly higher surface and transport wind speeds on Saturday will improve dispersion to the fair to generally good range. Moisture steadily increases across region, with rain and storm chances increasing through the weekend. Any storms that manage to develop will be capable of producing frequent lightning strikes, high wind gusts, and heavy downpours.

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 95 75 94 74 / 30 30 60 50 SSI 92 80 93 78 / 10 10 30 20 JAX 94 76 94 75 / 40 20 50 20 SGJ 91 76 93 75 / 30 10 40 20 GNV 94 73 93 73 / 60 40 60 20 OCF 92 73 92 74 / 80 30 70 30

JAX WATCHES/WARNINGS/ADVISORIES

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