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

- Numerous Afternoon and Evening Thunderstorms Expected through Saturday. Strong Storm Potential Along the I-95 Corridor During the Late Afternoon Hours. Stronger Storms May Produce Wind Gusts of 40-55 mph, Frequent Lightning Strikes, and Torrential Downpours that Could Result in Localized Flooding.

- Daily Peak Heat Index Values of 104-108 Degrees Expected. through Monday.

- Moderate Rip Current Risk Continues at All Area Beaches through Monday. High Risk Likely from Tuesday through Thursday of Next Week.

NEAR TERM /THROUGH TONIGHT/

Main Highlights:

- Potential for strong thunderstorms and localized flooding this afternoon and evening, especially along the I-95 corridor.

- Moderate Rip Current Risk at All Area Beaches.

Mean layer ridge oriented more or less west-east through 700 mb is located in central FL area. Typically for September this ridge is located further north. Deep layer flow is southwesterly at about 10 kt, and we continue with the deep moisture in place with the 18z JAX Sounding showing 2.29 inches and 500 mb temp of only -4.1C. Fairly confident PWATS will stay the same today, but the 500 mb temps may drop another degree or so during the day. Models suggest that some shortwave energy may impinge on the forecast area after 21z today which will likely encourage more cloudiness and probably boost rain chances this evening.

Given the moisture and summer-like pattern, we anticipate scattered to numerous showers and storms to develop during the day. Initial develop of convection likely to be around any lingering boundaries from Thursday, and along the west and east coast sea breezes that develop by the early afternoon. Climatology would suggest the I-75 corridor first, though, near the developing west coast sea breeze. The movement of the west coast sea breeze may meet the east coast sea breeze this afternoon and early evening, and cells mergers may would be near and east of the U.S. Highway 301 area. The moisture laden airmass will be efficient for heavy rainfall/localized flooding. Rain amounts in excess of 3 inches in spots are likely. The DCAPE on the model soundings looks unimpressive at about 500-600 J/kg, similar to yesterday, so for now assuming peak thunderstorm gusts of about 40-50 mph. Cannot totally rule out an isolated severe storm though where strongest convergence occurs.

Daytime highs will be in the lower 90s, and probably around 90 at the east coast as the sea breeze develops. Heat index values will hover under Heat Advisory criteria, with values in the 104-108 F range. Lows tonight in the lower to mid 70s.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/

Main Highlights This Period:

- Potential for strong thunderstorms and localized flooding on Saturday afternoon and evening, especially along the I-95 corridor.

Scattered to numerous showers and storms are anticipated on Saturday as moist southwesterly flow, with PWAT values of 2 to 2.3 inches, continues to move over the region from out of the Gulf. There is a potential for heavy rains and localized flooding for storms developing along the sea breeze boundaries and areas of convergence, likely along and west of the I-95 corridor. Convection is expected to be less widespread on Sunday as the high pressure ridge shifts northward and crosses over the forecast area, with the prevailing flow gradually shifting to a more northeasterly onshore flow by the beginning of next week. High temperatures will rise up into the lower 90s this weekend with overnight low temperatures dropping down into the lower to mid 70s over inland areas and int the mid to upper 70s for areas along the coast. Heat index values today will rise to over 100 with apparent temperatures potentially reaching as high as 110 for northeast Florida, however conditions are anticipated to remain below heat advisory criteria. Potential for patchy early morning fog and low cloud decks over inland areas before and around sunrise during the overnight and early morning hours this weekend.

LONG TERM /MONDAY THROUGH THURSDAY/

Main Highlights This Period Monday through Thursday:

- Daily Thunderstorms Potential Each Day Next Week.

- High Rip Current Risk Develops on Tuesday and Continues through at Least Thursday Next Week.

Northeasterly onshore flow will be in place through the latter part of next week as the axis of high pressure rotation settles in to the north. Chances for daily bouts of showers and storms will lessen for southeast Georgia and areas of northeast Florida north of the I-10 corridor as drier air advects into the forecast area from out of the northeast, with a higher likelihood of convection for areas south of I-10. Above average high temperatures reaching into the lower 90s will gradually drop down into the upper 80s and be nearer the seasonal average by midweek. Heat index values will drop down to be below 100.

Rip current risk will also become elevated rather than moderate as a result of the pattern shift.

AVIATION /12Z FRIDAY THROUGH 12Z SATURDAY/

VFR conditions will prevail at the regional terminals through at least 17Z. Showers and thunderstorms will begin developing near the Duval County terminals, SSI, and SGJ towards 18Z, with activity then reaching the GNV terminal after 19Z. TEMPO groups for brief surface wind gusts up to 25 knots and IFR conditions during heavier downpours were placed in the TAFs at all terminals through around 00Z. Convection may linger at the Duval County terminals, SGJ, and SSI through around 03Z this evening, where PROB30 groups for brief surface wind gusts up to 25 knots and IFR visibilities during heavier downpours were used during the evening hours. VFR conditions should then prevail at the regional terminals before 04Z Saturday. MVFR to IFR visibilities are then likely to develop at VQQ after 07Z, with confidence only high enough to forecast prevailing MVFR visibilities at this time. Southwest to westerly surface winds around 5 knots will develop towards 14Z, followed by south to southwesterly winds increasing to 5-10 knots by 16Z. The Atlantic sea breeze will develop before 18Z and will move slowly inland this afternoon, shifting surface winds to southeasterly around 10 knots at the SSI and SGJ coastal terminals before 19Z. Surface winds will diminish at the inland terminals following the conclusion of convection by 03Z, while south to southwesterly surface winds remain sustained around 5 knots overnight at the coastal terminals.

MARINE

Atlantic high pressure ridge will be centered from Bermuda to central Florida through early next week. This will favor prevailing southwest to south winds the next few days but the afternoon sea breeze will shift winds to southeast each afternoon across the near shore waters. Thunderstorms will likely develop over coastal locations during the afternoon hours and will shift eastward across our local waters during the afternoon and evening hours through the weekend. Onshore winds are forecast to develop Tuesday, with breezy conditions and building seas forecast towards Tuesday and Wednesday of next week.

Rip Currents: Generally offshore flow and weakening surf conditions suggest continuing a moderate risk today, with a lingering 2 foot wind-sea swell of about 7-8 seconds. This trend continues into the weekend likely maintaining a low to moderate risk. An increased threat of dangerous rip currents possible on Tuesday into Wednesday.

FIRE WEATHER

Diurnal southwesterly winds will persist through the end of the week and through the weekend. As a result of the moist southwesterly flow, the diurnal east coast sea breeze will be pinned near the shoreline and not reach inland much past the I-95 corridor. Flow pattern is expected to shift to become more onshore by the beginning of next week.

Fog Potential: Gusty and erratic wind shifts will occur from thunderstorm activity. Patchy fog is expected across inland areas the next couple of mornings, with widespread dense fog unlikely.

HYDROLOGY

As far as coastal water levels, coastal water levels will remain near and below action stage despite the new moon phase today.

As far as rainfall again today, isolated pockets of up to 3-4 inches are possible mainly the St Johns River Basin northward to near or just south of Waycross and Nahunta. These storms may cause temporary flooding, especially in any poor drainage or urbanized areas.

PRELIMINARY POINT TEMPS/POPS

AMG 91 73 91 73 / 50 20 50 20 SSI 90 77 89 76 / 40 30 50 20 JAX 91 74 91 74 / 60 40 70 10 SGJ 90 75 90 75 / 60 30 60 10 GNV 91 73 91 73 / 60 20 70 20 OCF 92 74 92 74 / 60 20 70 20

JAX WATCHES/WARNINGS/ADVISORIES

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