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. Severe Storm Risk Sunday Afternoon & Evening Southeast GA. Localized Flooding Rain Risk through Monday

- Patchy Inland Late Night & Early Morning Fog

UPDATE

Patchy to areas of fog and low stratus are starting to lift out of the area. But mostly little change to the ongoing forecast for today, which shows scattered convection developing through the late morning mainly over northeast FL, and at times numerous near the I-75 corridor south of Lake City southeast to Putnam to Flagler counties. Little changes were made to try to refine the greater chances of convection later today. Essentially no change to the forecast tstorms threats/afternoon time frame, with guidance and observations showing MLCAPE reaching upwards of about 2000 J/kg, probably a little higher for inland parts of northeast FL southwest of JAX metro area. This decent instability along with pockets of some slightly drier air aloft will result in probably a gustier t-storm wind threat compared to yesterday, mainly across the south tier of our counties. Probably looking at wind potential to about 40-50 mph and again heavy rainfall threat.

Updates were sent with some other minor changes for the sky and temps.

NEAR TERM /THROUGH TONIGHT/

Highlights Through Tonight:

- Isolated/Widely Scattered Thunderstorms, Mainly Over Northeast FL

The area will be under the influence of a very weak pressure gradient today, as ridging overhead weakens further as a frontal boundary approaches the area from the north tonight. High pressure centered to the east/southeast will result in a mainly west to southwest flow though generally weak around the 5 mph range except near the coast and St Johns River Basin area where it will be a bit stronger with a developing sea breeze. This breeze is not expected to make it much further west that about the I-95 corridor this afternoon.

With PWATs being lower today (closer to "only" 2 inches") and a bit of drier air aloft trying to filter into southeast GA, convective coverage looks to be overall more scattered today, and mainly found across northeast FL. The vertical profile and setup therefore does not stand out regarding stronger t'storm potential, though as per usual with sea breeze convection, isolated gusty downbursts and/or minor flooding cannot be ruled out, especially where boundary collisions occur. Light west/southwest flow will result in low 90s being common across the area today, with some mid 90s possible across inland GA where lower cloud/storm coverage will be.

Tonight, a few showers streaming off the Gulf in the southwest flow could make it towards the I-75 corridor at times, with otherwise daytime convection coming to an end by around the 10pm time frame. Lows will bottom out in the mid 70s for most.

SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/

Main Highlights This Period: (Sunday through Monday night)

- Localized Flooding Rain Threat

- Isolated Severe Storm Risk Southeast GA Late Sunday

A more dynamic period as a surface front edges southward across the local area late Sunday into Sunday night, then lingers across northeast FL Monday bringing more widespread rainfall and the risk of strong to severe storms. Aloft, a deepening mid level trough carves southward down the US Atlantic seaboard. The phasing of the upper level trough over the surface front late Sunday into Sunday night will bring the risk of a few late day and overnight strong to severe storms, in what could be an MCS like system, moving from the northeast over the Carolinas toward the south-southwest toward southeast GA.

The stronger upper level shear remains to the northeast of the region, but high surface based instability combined with the cooler mid level temps, steeping mid level lapse rates and increasing PVA aloft will bring the risk of gusty downburst winds across southeast GA Sunday evening through about midnight. At this time, severe storm risk looks more limited across northeast Florida as the airmass will have been 'worked out' by more typical sea breeze convection earlier in the day, with a dominant west coast sea breeze regime.

Monday, the surface front is expected to be lingering near the GA-FL state-line or across northeast Florida as high pressure northeast of the region begins to wedge southward across north GA. Aloft, the mid level trough lingers. This pattern could lead to broad surface lows forming near to just offshore of the local Atlantic coast for the early part of next week within an inverted coastal trough. Waves of gusty coastal showers and isolated storms will move onshore and expand in coverage as they shift inland with daytime heating into Monday afternoon toward the I-75 corridor into Monday evening.

Monday night, the ridge to the northeast expected to settle farther southward, with strengthening NNE to ENE winds along the coast into Tuesday morning and continuing coastal showers and isolated storms overnight as the surface front is shunted a little farther south toward north-central Florida.

The Weather Prediction Center maintains a Marginal Risk (level 1 out of 4) of localized flooding rainfall both Sunday and Monday across the local area. In addition, the Storm Prediction Center has a Marginal Risk of severe storms for southeast GA Sunday evening (level 1 out of 5).

Temperatures will top out in the low to mid 90s Sunday before showers and storms ensue with heat index values topping out near 105 degF, just below local Heat Advisory criteria. Monday, cooler with onshore easterly flow with highs in the 80s for most locations to near 90 toward the I-75 corridor due to clouds cover and convection. Lows will range in the 70s each night.

LONG TERM /TUESDAY THROUGH FRIDAY/

Main Highlights This Period: (Tuesday through Saturday)

- Breezy Onshore Winds Tuesday & Wednesday,

- Warm-Up Late Week

- Daily Thunderstorms Chances

- Elevated Tidal Levels with Approach of Sept 11 New Moon

Breezy northeast to east winds Tuesday and Wednesday as the coastal trough lingers over the adjacent coastal waters. This will bring coastal showers and isolated storms onshore, with coverage expanding inland each afternoon into the early evening across inland areas with diurnal instability. Aloft, the upper level trough axis shifts downstream and weakens with more stable conditions aloft favoring a lower severe storm risk. Thursday into Friday the surface high builds east then southeast of the region, with a return of westerly steering flow across the local area and a more dominant west coast sea breeze regime. Temperatures warm as highs rebound back into the lower 90s, just above climo values. Friday into Saturday, extending models are showing another front approaching from the north, but differ on the timing and mid level synoptic features. At this time, NBM consensus favors the front edging southward across the area late Friday into Saturday, with a return of easterly flow by Saturday with scattered showers and storms.

AVIATION /12Z SATURDAY THROUGH 12Z SUNDAY/

Main areas of low cigs or vsby restrictions are from about I-10 northward so affecting VQQ, JAX, and SSI terminals. Expect some period of IFR and LIFR for these terminals through about 14z. Lower chance of any cig or vsby issues for SGJ and GNV, and CRG early this morning. Cigs should lift out mid morning but some MVFR cig probabilities remain 14z-16z. Will again see fairly quick development of showers and storms, but mainly for the northeast FL area today. Good chances expected for SGJ and GNV, with slightly lower chances for the Duval county terminals. May able to only show just VCSH or a VCTS for SSI where the chances are much lower compared to northeast FL. Expect fairly quick-end to convection by about 23z/00z. Some patchy fog and low stratus possible again early Sunday morning, but does not look to be widespread or quite as much as this morning so may only show MVFR cigs or vsby, at best, for now. Sfc winds will be west to southwest about 5-10 kt later today, with sea breeze wind shift probably for SGJ and SSI this afternoon.

MARINE

Weak high pressure will remain in place through tonight before a frontal boundary sinks south across area Sunday through Monday night. High pressure will build to the northeast following the front early next week with a coastal trough over the local waters. A brief period of Small Craft Exercise Caution conditions is possible mainly over the Georgia waters Tuesday. The trough weakens mid- week as high pressure builds south of the region. Another front approaches from the north early next weekend.

Rip Currents: Rip current risk will remain moderate across northeast FL beaches through the weekend with lingering long period swells and a developing onshore flow each afternoon and evening. The risk will be slightly lower at southeast GA beaches.

FIRE WEATHER

- Patchy Low Dispersions Ne Fl Monday

West to southwest winds this weekend will bring a more dominant west coast sea breeze 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. There is a risk of stronger to severe storms late Sunday into Sunday night across southeast Georgia as a front moves into the area. The front is expected to linger across northeast Florida Monday, which will create low daytime dispersion, more cloudiness and bring elevated rain chances through the day. Winds will transition to northeast along and north 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 next 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. At this time, 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.

PRELIMINARY POINT TEMPS/POPS

AMG 92 75 95 73 / 20 20 70 80 SSI 91 77 93 75 / 10 20 60 80 JAX 91 75 93 74 / 30 20 50 60 SGJ 90 76 93 75 / 50 20 60 60 GNV 90 74 92 73 / 60 10 40 50 OCF 90 74 92 74 / 60 10 50 40

JAX WATCHES/WARNINGS/ADVISORIES

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