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

- Isolated Strong Storms Late this Afternoon Across Portions of North Central FL.

- Isolated to Widely Scattered Afternoon & Evening Thunderstorms Thursday.

- Dangerously Hot & Humid Conditions Late this Weekend. Heat Advisory Conditions Possible Sun & Mon, when Values Approach 110

- Minor Flooding Continues along the Satilla River in Southeast GA.

NEAR TERM /THROUGH TONIGHT/

Main Highlights through Tonight:

- Isolated Strong Storms Possible Late this Afternoon and Early this Evening Across North Central FL.

Afternoon surface analysis depicts a stationary frontal boundary positioned just south of Interstate 10, with weakening high pressure (1022 millibars) centered over the southern Appalachians and the Tennessee Valley in the wake of this boundary. Aloft...subtle troughing was sinking slowly southward across the FL peninsula, while stout ridging centered over west Texas and southern New Mexico was extending its axis southeastward along the northern Gulf coast. Latest GOES-East derived Total Precipitable Water imagery indicates that an unseasonably dry air mass continues to advect into our area from northwest to southeast, with PWATs falling to near 1 inch for locations along and north of Interstate 10, while values ranged from 1.5 to 1.75 inches across north central FL. A healthy cumulus field was developing over the more seasonably humid air mass across north central FL and also along portions of the I-95 corridor in northeast FL as the Atlantic sea breeze has begun to move inland. Dewpoints were falling through the 60s for locations along and north of I-10, while lower 70s prevail for coastal northeast as well as north central FL as of 17Z. Temperatures ranged from the mid 80s at coastal locations to the lower 90s across inland portions of northeast and north central FL.

A weak surface pressure pattern across our area will allow for sea and river breezes to propagate inland this afternoon, with deep- layered north-northwesterly flow continuing to advect an unseasonably dry air mass across southeast GA and northeast FL through tonight. Meanwhile, just enough moisture will remain across the Ocala National Forest and perhaps for other locations such as Flagler County in north central FL. Slightly cooler temperatures aloft associated with the weakening trough could allow for a few storms that develop across north central FL to briefly pulse to strong levels from late this afternoon through early this evening. Any stronger storms that manage to develop could produce downburst winds of 40-50 mph, along with cloud to ground lightning strikes and briefly heavy downpours. Any convection that manages to develop across north central FL should dissipate during the early to mid- evening hours tonight, with unseasonably dry weather otherwise continuing for the rest of our region.

Plenty of sunshine and the dry air mass in place across our region should allow highs to soar to the low and mid 90s at most inland locations this afternoon, but dewpoints falling through the 60s will keep heat index values close to actual air temperatures across southeast GA and northeast FL. Meanwhile, heat index values will climb to the 100-105 range across north central FL. An onshore breeze this afternoon will keep coastal highs in the upper 80s to around 90. Shortwave energy riding overtop of the ridge that extends along the northern Gulf coast will push cirrus cloud cover into our region overnight, which could prevent significant fog formation towards sunrise on Thursday. Diminishing winds and a lingering dry air mass should allow lows to fall to the upper 60s to around 70 for inland southeast GA and for inland locations along the I-10 corridor and Suwannee Valley, while lows across north central and coastal northeast FL remain in the low to mid 70s.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/

Main Highlights This Period:

- Widely Scattered Inland Afternoon and Evening Thunderstorms Thursday and Scattered to Numerous Storms Closer to I-95 and Coastline Friday.

- Seasonably Hot and Humid Weather Thursday and Friday.

Thursday: Reverting back to a more typical summertime convective pattern as the stalled frontal zone dissolves through the morning, leaving a light southwesterly flow in place. Lingering dry mid level will moisten up late in the day but should minimize t'storm coverage, focusing the best potential for scattered thunderstorms generally along the US 301 corridor where the Gulf and Atlantic sea breezes will zipper south to north during the late afternoon and early evening hours. While the typical downward trend will occur after sunset Thursday, a few outflow interactions may keep showers and an isolated storms possible across SE GA until midnight. Temperatures will bounce back quickly with highs in low 90s and heat index readings back into the 100s.

Friday: Southwesterly flow will increase while deep moisture also increase. Pushing the focus and better chances for strong convection eastward to the I-95 corridor and coastal areas Friday afternoon and evening. Despite some warming aloft as the upper ridge centered east of the Bahamas exerts its influence, instability should still be at moderate levels and sufficient for strong pulse storm development. Warming trend continues into Friday with highs again pushing toward the mid 90s. Better mixing with a breezier southwesterly flow should keep heat index from pushing into the Heat Advisory range but increasing coverage in 100-105 degree "feels like" temps are expected.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Main Highlights This Period:

- Heat Advisory Considerations Saturday, Sunday, and Monday.

- Lower than Usual Confidence For Storms Saturday through Sunday, with Numerous T'Storms Returning Monday.

Upper ridging will consolidate over the weekend with amplified ridging developing over the Mississippi River Valley where it will meander through next week. The position of the ridging puts the region on the southeastern periphery and leaves the door open to glancing shortwave or "ridge riders" early next week. Two considerations with the current forecast is significant model disagreement regarding deep moisture and the potential convective suppression beneath the congealing upper ridging. Right now, have maintain isolated to widely scattered afternoon t'storm potential over the weekend but an upward trend is possible if deeper moisture ends up trapped beneath the ridge. With the lower rain chances and warming low level temps, climbing above the climatological 90th percentile, will support temperatures climbing into the mid and upper 90s over the weekend which may require "Heat Advisory" considerations, especially on Sunday.

By early next week a backdoor front will attempt to slide into the area from the northeast and possibly stall over the area through the first half of next week. Moisture pooled with the front and a "ridge rider" mid level wave will set up the potential for scattered to numerous t'storms and potential for strong to severe storms on Monday. Convective timing will influence temperatures on Monday but expect dangerous levels of heat to continue. A breezy onshore flow and abundant cloud cover along the stalled front should keep temperatures more seasonal Tuesday and Wednesday, especially at the coast.

AVIATION /18Z WEDNESDAY THROUGH 18Z THURSDAY/

VFR conditions will prevail through at least 07Z at the regional terminals. Fog will develop after 07Z at VQQ, where we have indicated prevailing MVFR visibilities, with periods of IFR visibilities likely after 09Z as high cloud cover potentially thins out and shifts south of our region. A period of MVFR visibilities was also indicated at GNV around sunrise as high cloud cover shifts south of the terminal. Fog will be possible elsewhere during the predawn and early morning hours at the remainder of the terminals, but confidence was too low to indicate sub-VFR visibilities at this time. The Atlantic sea breeze boundary will continue to shift inland as the afternoon progresses, with easterly surface winds remaining sustained around 10 knots at SGJ through around 00Z, while southeasterly surface winds around 10 knots prevail at SSI. Light northwesterly surface winds elsewhere should continue through around 20Z, with winds at the Duval County terminals then shifting to northeasterly and easterly and increasing to 5-10 knots late this afternoon and early this evening as the sea breeze pushes westward. Surface winds will tend to shift to southerly or southwesterly after 03Z while diminishing. Southwesterly surface winds will then resume towards 14Z Thursday, with speeds increasing to 5-10 knots by 16Z.

MARINE

A weakening frontal boundary positioned over the northeast FL waters will dissipate tonight. Isolated showers and thunderstorms will be possible this evening, mainly for the waters south of St. Augustine. A weak pressure pattern will continue through Thursday, allowing for the Atlantic sea breeze to move onshore during the early evening hours. Atlantic high pressure will then extend its axis westward across the Florida peninsula from Friday through Sunday, creating a prevailing westerly wind flow during the overnight and morning hours, with winds becoming onshore each afternoon as the Atlantic sea breeze moves inland. Scattered showers and thunderstorms are expected to impact our local waters during the late afternoon and evening hours each day from Thursday through Sunday. A surface trough will then press southward across our area on Monday, providing an increasing coverage of showers and thunderstorms. Northeasterly winds will develop by Monday night and Tuesday as this trough shifts southward and high pressure builds over the southeastern states, with breezy conditions possible by Tuesday afternoon.

Rip Currents:

A lower end moderate risk will develop during the late afternoon hours each day through Friday at area beaches as onshore winds become breezy following the passage of the sea breeze. A developing southeasterly ocean swell will combine with onshore winds developing during the mid to late afternoon hours this weekend to maintain a lower end moderate risk at all area beaches.

FIRE WEATHER

After seasonably low humidity this afternoon, humidity will trend higher and back to typical levels through the end of the week as the remnant front dissipates over the area. Returning moisture will support afternoon thunderstorms along the sea breezes with best chances lining up where the Gulf and Atlantic sea breezes are expected to converge, which appears to be along the US 301 corridor Thursday and then the I-95 corridor Friday. Potential for less thunderstorm activity over the weekend with heat building back to the mid 90s. More active thunderstorm pattern becoming more likely Monday as a backdoor front enters the area. Hotter temperatures and increasing southwesterly flow Friday may lead to areas of higher dispersion, mainly inland toward the I-75 corridor.

FOG POTENTIAL AND OTHER REMARKS: Dense fog is not expected, but shallow fog formation is possible.

HYDROLOGY

Minor flooding continues along the Satilla River Basin, with water levels forecast to fall below flood stage at the gauge near Waycross by early Friday evening. Minor flooding will continue downstream near the gauge at Atkinson during the next several days.

PRELIMINARY POINT TEMPS/POPS

AMG 69 93 73 93 / 10 20 30 20 SSI 76 90 79 92 / 10 20 10 30 JAX 71 95 76 96 / 10 50 10 40 SGJ 74 93 77 94 / 10 40 10 30 GNV 71 96 74 96 / 10 20 10 30 OCF 72 95 75 95 / 20 30 10 30

JAX WATCHES/WARNINGS/ADVISORIES

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