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 Afternoon & Evening TStorms Saturday. Strong to Isolated Storms Possible. Hazards: Winds of 40-60 mph, Frequent Lightning Strikes & Heavy Downpours. Isolated to Widely Scattered Afternoon & Evening TStorms Expected on Sunday

- Hot & Humid Conditions through Monday. Heat Advisories Possible Mon, when Afternoon Heat Indices Peak at 105 - 110 F

- Numerous TStorms Expected on Monday Afternoon & Evening

- Minor Flooding Continues along the Satilla River in Southeast GA

UPDATE

While most of the stronger convection has simmered down in the last hour or so, lingering showers and isolated storms will continue through the evening. Tonight, mild lows in the lower to mid 70s inland and near the upper 70s along the immediate coast and St. Johns river basin.

SHORT TERM /THROUGH SUNDAY NIGHT/

Main Highlights This Period:

- Scattered Afternoon and Evening Thunderstorms on Saturday

- Thunderstorm Coverage Decreases Somewhat on Sunday - Summertime Heat and Humidity Builds this Weekend, with Heat Advisory Conditions Possible on Sunday Afternoon

Our region will be positioned between a building "Heat Wave" ridge and a flattening Atlantic ridge aloft on Saturday, with low and mid level southwesterly flow continuing across our area as surface ridging continues to extend its axis westward across the FL peninsula. Mid-level flow will tend to veer to a more westerly direction as ridging to our west becomes amplified by late Saturday afternoon and evening. Strengthening subsidence associated with this building "Heat Wave" ridge over the Mississippi Valley will tend to limit diurnal convective activity across inland southeast GA and northern portions of the Suwannee Valley. Scattered convection is expected elsewhere, with a dominant Gulf coast sea breeze developing activity along the I-75 corridor in north central FL during the early afternoon hours, with a few stronger storms potentially developing for locations along and east of the U.S. Highway 301 corridor in northeast and north central FL as mesoscale boundaries such as the Atlantic sea breeze and the St. Johns River breeze interact with convection approaching from the west and southwest. Heights aloft will begin to rise as ridging builds to the west of our area, and highs will soar to the low and mid 90s all the way to coastal locations as prevailing southwesterly flow tends to "pin" the Atlantic sea breeze along and east of I-95 through the mid- afternoon hour. The combination of heat and humidity will create peak heat indices of 100-108 degrees on Saturday afternoon, which means that a few locations could approach Heat Advisory criteria.

Convection should remain largely diurnal in nature this weekend, with activity along the I-95 corridor winding down around or shortly after sunset both on Saturday and Sunday. Coverage may decrease slightly on Sunday as ridging aloft strengthens over the lower Mississippi Valley and expands southeastward into our area. However, enough moisture will remain in place for isolated to widely scattered thunderstorms to develop, mainly for locations along and east of U.S. Highway 301 in southeast GA, northeast and north central FL, where mesoscale boundaries will collide during the mid to late afternoon hours. Less convective coverage and increasing subsidence, supplied by the "Heat Wave" ridge to our west will allow highs to soar to the mid and upper 90s across most of our area, with Heat Index values potentially peaking in the 105-110 degree range that would prompt Heat Advisories for at least portions of our area. Overnight lows on Saturday and Sunday nights will only fall to the mid or upper 70s at most locations.

LONG TERM /MONDAY THROUGH FRIDAY/

Main Highlights This Period:

- Heat Advisory Conditions Possible Monday.

- Numerous Thunderstorms on Monday, with Strong Storm Potential During the Afternoon and Evening Hours

- Temperatures Cool Slightly on Tuesday and Wednesday as a "Backdoor" Frontal Boundary Stalls Over Our Area

"Heat Wave" ridging centered over the lower Mississippi Valley on Monday will migrate northward towards the Tennessee and Ohio Valleys by midweek, allowing for troughing and a "backdoor" frontal boundary to progress southward down the southeastern seaboard, with this boundary expected to stall over northeast or north central FL by Tuesday before dissipating on Wednesday. Oppressive heat and humidity will precede the arrival of this "backdoor" front on Monday, with highs again soaring to the mid and upper 90s, with Heat Index Values peaking in the 106-112 degree range across our area, likely prompting Heat Advisories for Monday afternoon. Strong storms will likely erupt in this hot and increasingly unstable air mass on Monday afternoon and evening, with some potential for isolated severe thunderstorms that could produce downburst winds in excess of 60 mph.

Surface high pressure building along the Mid-Atlantic coast in the wake of this "backdoor" frontal boundary will shift low level flow to easterly on Tuesday and Wednesday. The stalling boundary over our area on Tuesday will keep numerous showers and thunderstorms in the forecast, with activity potentially beginning early in the day along the I-95 corridor and then progressing inland towards the I-75 corridor and inland southeast GA during the afternoon. Locally heavy downpours and a few stronger wind gusts will be possible, especially at inland locations. Increasing cloud cover and high rain chances will keep temperatures in the upper 80s and lower 90s on Tuesday and Wednesday , providing a nice break from the oppressive heat and humidity that is forecast on Sunday and Monday. A drier air mass may then briefly advect into our area towards midweek, with prevailing low level easterly flow concentrating convection across inland north central FL and southern portions of the Suwannee Valley. Isolated to widely scattered showers and thunderstorms may continue into Thursday and next Friday as a drier air mass potentially lingers, but temperatures may be trending higher towards the Independence Day weekend as the "Heat Wave" ridge positioned over the Ohio Valley around midweek potentially expands east and southeastward.

AVIATION /00Z SATURDAY THROUGH 00Z SUNDAY/

VFR conditions expected other than some MVFR visibilities at SSI due to lingering light showers, and vicinity light showers elsewhere this evening. Winds will continue to calm after sunset, and pick up again from the southwest after sunrise. Have places VCTS in the TAFs beginning around 18-20Z for the northeast FL sites, excluded SSI due to lower probabilities there at this time.

MARINE

Atlantic high pressure will extend westward across the Florida Peninsula just south of the area waters through the weekend. A pattern of overnight to early morning light westerly offshore winds and afternoon southeasterly winds expected due to sea breeze circulations. Afternoon and early evening isolated to scattered storms will develop across the nearshore waters each day into Sunday. A weak back door frontal boundary will approach the waters on Monday, supporting increased coverage for showers and thunderstorms for the first part of early next week.

Rip Currents:

A lower end moderate risk will develop into this weekend 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

Scattered to numerous showers and thunderstorms will shift east- northeastward across our area this afternoon and evening, with strong to isolated severe storms possible along the U.S. Highway 301 and Interstate 95 corridors. Coverage of afternoon and evening showers and thunderstorms will diminish somewhat this weekend, with activity tending to cluster at locations along and east of U.S. Highway 301. Thunderstorm coverage will then increase on Monday afternoon and evening area-wide, with strong storms possible. Otherwise, southwesterly transport winds this afternoon and tonight will shift to westerly this weekend and then west- northwesterly on Monday. The Atlantic and Gulf sea breezes will develop and progress inland each afternoon, resulting in surface winds becoming southeasterly for locations along and east of I-95 during the early to mid afternoon hours each day. Elevated mixing heights will generally yield fair to good daytime dispersion values at inland locations, with fair values expected at coastal locations. FOG POTENTIAL AND OTHER REMARKS: Significant fog is not expected the through the weekend. Stronger thunderstorms this afternoon and evening and again on Monday afternoon and evening will be capable of producing wind gusts of 40-60 mph, frequent cloud to ground lightning strikes, and locally heavy downpours.

PRELIMINARY POINT TEMPS/POPS

AMG 73 93 75 95 / 20 20 10 10 SSI 78 92 79 95 / 30 20 10 20 JAX 75 96 76 97 / 20 30 20 40 SGJ 76 94 76 95 / 40 30 20 20 GNV 73 95 74 96 / 10 40 20 20 OCF 74 94 74 95 / 10 40 20 20

JAX WATCHES/WARNINGS/ADVISORIES

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