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

- Moderate Rip Current Risk Northeast FL Beaches this Weekend

- Daily Heat Index near 105 through the Weekend

- Daily Afternoon/Evening Thunderstorms Through Next Week. Strong/Severe Storm Risk this afternoon and evening. Localized Flooding Rain Risk through Monday

- Patchy Inland Late Night & Early Morning Fog

NEAR TERM /THROUGH TONIGHT/

Highlights Through Tonight:

- Hotter with Peak Heat Index near 105

- Severe Thunderstorm Risk this Afternoon & Evening

Light westerly steering flow this morning will strengthen into the afternoon as an upper level trough deepens over the eastern US and drives a surface front southward toward the area. This front, combined with sea breezes and upper level forcing over a very unstable airmass will phase across the coastal Carolinas and Georgia this afternoon, with resultant strong to severe storms tracking northeast to southwest across the local area through this evening.

Before the risk of severe storms increases mid afternoon, diurnally driven airmass and sea breeze showers and storms begin to develop across the local along both the Gulf and Atlantic coast sea breezes as well as along a lingering outflow boundary poised to position near the FL-GA state line by the early afternoon. As boundary mergers occur along the sea breezes and near the lingering outflow boundary, the risk of strong to pulse severe storms increases near and east of the Highway 301 corridor toward the Atlantic coast late afternoon into the early evening. Then the focus for strong to severe storms shifts toward the Altamaha River basin and much of southeast GA by early evening as the surface front and a line of convection approaches from the northeast. This activity will track from northeast toward the south-southwest through midnight, with southward momentum slowing as diurnal instability fades and a vorticity maximum within the mid level trough shifts farther offshore of the southeast seaboard. Showers and isolated storms will be possible after midnight, but storm severity will fade as the surface front begins to stall and linger near the FL-GA state line or northeast Floria.

The greatest hazards in strong to severe storms this afternoon and evening will be damaging downburst winds and locally heavy, briefly flooding rainfall. The stronger severe storm wind threat will focus near the Altamaha River Basin across southeast GA this evening where downdraft CAPE is forecast to reach 800-1000 J/kg with surface temperatures reaching the mid 90s before the onset of convection. This environment will favor strong storm outflows/cold pools, with additional storms developing along fast-moving gust fronts pressing southward across GA this evening toward the FL Interstate 10 corridor a few hours after sunset. The Storm Prediction Center maintains a 'Slight Risk' (level 2 out of 5) of severe storms near the Altamaha River basin and a 'Marginal Risk' (level 1 out of 5) across the remainder of southeast Georgia toward the north Florida Interstate 10 corridor.

With multiple boundary mergers and upper level lift, the Weather Prediction Center has upgraded portions of southeast GA to a "Slight Risk" (level 2 out of 4) of flash flood risk for storms this afternoon into the evening. Anticipated rainfall through tonight is generally 0.25 to 1 inch north of I-10 toward the Atlantic coast, with higher end totals of 3-4 inches possible especially across portions of southeast GA.

Have a way to monitor for warnings this afternoon and into the evening, including after sunset. Be ready to quickly shelter indoors when storms threaten this afternoon and into the evening.

With warm, westerly flow temperatures will trend warmer today and above climo values for early September with highs topping out in the low to mid 90s. Heat index values will peak right around 105 deg early to mid afternoon for locations east of Highway 301, below local heat advisory criteria. Tonight, overnight lows will range in the low 70s inland to mid 70s coast. Less fog potential tonight due to abundant cloud cover.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/

Main Highlights This Period:

- Localized Flooding Rain Threat

- Daily Thunderstorms Chances

A stalled cold front over the area on Monday will begin to shift towards north central FL by Tuesday. With elevated levels of moisture aloft and the proximity of the front, the coverage of numerous showers and storms is expected to span across the area on Monday and Tuesday. The highest chances will generally be during the afternoon and evening each day, with some activity lingering during the overnight hours Monday to Tuesday. Behind the front, stronger onshore flow will direct offshore activity back towards the coast and then inland locations by the afternoon hours. Gusty conditions can be expected for coastal locations with the stronger onshore flow, particularly for SE GA.

With the cold front making its way across the area, cooler temperatures will develop from north to south. On Monday, SE GA locations will likely top out in the upper 80s, while NE FL will be in the upper 80s to lower 90s. By Tuesday, highs in the mid to upper 80s will develop behind the front.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

Main Highlights This Period:

- Daily Thunderstorms Chances

- Elevated Tidal Levels with Approach of Sept 11 New Moon

Behind the front, relatively drier air (PWATs 1.8" to ~2") filters into the area by midweek. With drier air moving in, chances of precipitation will steadily lessen through the end of the week. During midweek, the continuing onshore flow will steer any showers and storms towards inland located during the afternoon hours. Southerly then southwesterly flow develops by the end of the week. Guidance suggests another cold front will push towards the SE US by the upcoming weekend as high pressure develops north of the area along the eastern seaboard.

Temperatures in the mid 80s to lower 90s midweek behind the front, will begin to increase back to near normal levels as southwesterly flow develops heading into next weekend.

AVIATION /06Z SUNDAY THROUGH 06Z MONDAY/

Prevailing VFR tonight but the usual suspect VQQ may drop visibility. Prevailing westerly winds 3-8 kts through the morning with diurnally driven cumulus developing late morning possibly causing brief MVFR restrictions. Winds become SSE at coastal terminals SSI, CRG and SGJ between 16-18z with the east coast sea breeze. Shower and thunderstorm chances increase this afternoon and continue into the evening. Continued with PROB30 and TEMPO groups to reflect when most confident with TS impacts at and near the terminals. TSRA risk and associated impacts continue after 00z this evening through about 04z as a surface front slides southward across the local area.

MARINE

High pressure will continue south of the local waters today as a front approaches from the northeast. Strong thunderstorms are possible this afternoon and evening as the front approaches. The front will stall across north Florida Monday, then shifts south of the waters Monday night into Tuesday as high pressure strengthens to the northeast. A brief period of Small Craft Exercise Caution conditions is possible mainly over the Georgia waters Tuesday as a coastal trough develops offshore. The coastal trough weakens Wednesday into Thursday. Friday into Saturday, high pressure extends across south Florida with a return of westerly winds and the afternoon east coast sea breeze nearshore.

Rip Currents: Will maintain a moderate rip current risk for northeast FL beaches given a small but consistent 10-14 second periods from the east. Low rip current risk for southeast GA beaches today. Rip current risk increases from north to south Monday as onshore flow develops with moderate risk likely for all local beaches. By Tuesday, solid moderate to possibly high rip current due to stronger and more persistent ENE onshore winds.

FIRE WEATHER

- Patchy Low Dispersions Northeast Florida Monday And Tuesday

West to southwest winds continue Today allowing for the west coast sea breeze to push across the area. Morning showers and isolated storms will begin to move inland form the Gulf, with rainfall expanding in coverage into the afternoon and early evening across inland areas toward the Atlantic coast where the east coast sea breeze will be near the Interstate 95 corridor to the coast. A risk for stronger to severe storms Tonight across southeast Georgia with a stalled front over the area. The front is expected to shift southward across northeast Florida Monday, with low daytime dispersion, more cloudiness and bring elevated rain chances through the day. Winds will transition to northeast behind of the front Monday.

Fog Potential: Gusty and erratic winds will occur with thunderstorm activity. Patchy inland morning fog each day.

HYDROLOGY

Coastal water levels begin to increase this week with the approach of the New Moon on Sept 11th and breezy onshore easterly winds late Monday through Wednesday, with the peak winds across the local waters and coast Tuesday. Extended probabilistic guidance keeps water levels below action stage late Tuesday through Wednesday both along the local Atlantic coast and within the St. Johns River basin with minimal local tidal water impacts.

PRELIMINARY POINT TEMPS/POPS

AMG 94 73 87 72 / 50 80 80 30 SSI 92 76 86 77 / 50 80 90 70 JAX 93 73 88 73 / 50 70 90 50 SGJ 92 74 88 74 / 50 70 90 60 GNV 92 73 89 72 / 40 40 100 60 OCF 92 74 90 73 / 30 50 90 50

JAX WATCHES/WARNINGS/ADVISORIES

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