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 Thunderstorms each day this week. Main hazards will be wind gusts up to 50 mph, frequent lightning, locally heavy rainfall. Main area for stronger thunderstorms today will be east of Highway 301 toward the coastline.

- Hot and Humid Conditions Continue this Week. Heat Advisory headlines possible as heat indices climb to near 105 to 110 late this week.

NEAR TERM /THROUGH TONIGHT/

Main Highlights Today and Tonight:

- Isolated Strong T'Storms 3-6 PM Along/East of the I-95 Corridor - Hot Conditions with Heat Index in the 102-108 Degree Range

Hot and humid conditions early this afternoon have pushed heat index values into the upper 90s and low 100s. Ample surface-based instability across inland areas has begun to "seed" a few showers within the highly unstable airmass. An expanding shower coverage is expected through around 2 PM with isolated to scattered thunderstorms developing amid the seasonably moist westerly flow. For the most part, the concern for strong pulse convection will favor the the a north-south corridor along the St Johns River basin and the I-95 corridor. The best window for strong t'storms will be between 3 PM - 6 PM today.

Hot temperatures and the steep near-surface lapse rates will prime the potential for strong downbursts, especially with the first push of deep convection this afternoon; stronger pulses may be capable of gusts around 40-50 mph as they collapse. While at least minor flooding cannot be ruled out, the potential for flooding is on the low side given the well-paced westerly storm motion around 20 mph.

For tonight, any lingering convection that hasn't pushed into the Atlantic should fade after sunset. Skies will likely become mostly clear with muggy overnight lows in the middle 70s inland and upper 70s along the Atlantic Coast.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/

Main Highlights This Period:

- Lower storm coverage Tuesday & Wednesday

Showers and storms shift north to south Tuesday afternoon into the evening mainly impacting the middle section of the local forecast area between Waycross to the FL I-10 corridor where deeper moisture plume coincides along a southward moving washed-out frontal zone and passing upper level short wave trough. A few stronger storms and locally heavy rainfall are possible where sea breezes and frontal activity converges. Tuesday night, the front shifts farther south and begins to stall and linger across central FL. Wednesday, much drier air with PWAT < 10th percentile brings rain chances < 15% across inland southeast GA with the higher chances of afternoon and evening showers and storms south of Gainesville to St. Augustine southward and toward the Atlantic coast, with storm motion from the northwest to the southeast into the evening and clearing skies for much of the area by 8 pm.

Highs will range in the low/mid 90s with daily heat index values 95- 100 across most of southeast GA to around 105 degF across northeast FL. Muggy overnight lows will range in the 70s.

LONG TERM /THURSDAY THROUGH SUNDAY/

Main Highlights This Period:

- Daily heat indices 105-108 degF - Daily thunderstorm risk

Daily mainly afternoon and evening showers and storms will continue under active southwest steering flow and a more dominant west coast sea breeze regime through Sunday. Thursday will likely be a more active convective day with plenty of moisture in place and convection firing along both sea breezes and south of an approaching, weakening surface front under a passing mid level trough across the southeast region. Friday, the 1000-500 mb ridge axis begins to build westward across the central Fl peninsula, then by the weekend the ridge center positions across the northeast GOMEX. Elevated moisture will continue across the local area. This type of pattern favors higher rain chances toward the Atlantic coast, and could even bring a 'zipper' type of convection effect with diurnally enhanced convection across the Carolinas shifting southward down the sea breeze merger into the afternoon and evenings with isolated stronger storms and localized heavy rainfall possible. Inland areas will be drier under the influence of the upper ridge. Monday, the 1000-500 mb ridge center shifts northward, with a transition to a north to northeast steering flow and a return of a more dominant east coast sea breeze regime early next week.

Temperatures will moderate to near to above climo values with highs in the 90s and daily heat index values 105-108 degF, just barely at local heat advisory criteria of 108-112 degF. Muggy overnight lows will range in the 70s.

AVIATION /18Z MONDAY THROUGH 18Z TUESDAY/

Widely scattered showers are breaking out across the area early this afternoon with increasing confidence in a potential TSRA impacts, or at least +SHRA impacts through the afternoon hours with probability increase at airfields closer to the coast. Thunderstorms will have capacity to produce gusty, erratic winds but outside of that influence westerly winds 8-12 knots will prevail with gusts up to 20 knots. Bulk of the convection should occur between 19z-23z with fading showers through the evening. Overnight, there could be some MVFR low stratus inland and may reach KGNV by sunrise. Otherwise, VFR conditions with mid level cloud cover is expected overnight. Another round of similarly timed convection is expected Tuesday with a similar westerly flow.

MARINE

Prevailing offshore winds will keep seas low and maritime conditions fair. Offshore flow and unstable airmass will lead to daily potential for scattered thunderstorms during the afternoon and evening hours. A front will press into the waters and stall through Wednesday which lead to a break in the offshore flow pattern through Thursday before returning this weekend. While winds will be generally less than ten knots during the daytime, nightly southerly wind surges may lead to Exercise Caution Conditions offshore during periods of offshore flow.

Rip Currents:

Rip current risk is expected to remain on the low side with the predominant offshore flow and surf/breakers 1-2 ft through this week.

FIRE WEATHER

Breezy westerly winds near 10 to 15 mph with gust potential to 25 mph Tuesday ahead of a front that slowly edges southward across the area, with the best coverage of storms between Waycross and the I-10 corridor. Wednesday, the front begins to stall across north-central FL with much drier conditions across southeast GA but continued mainly afternoon showers and storms across northeast Florida, especially near the St. Johns river basin under northwest winds, with an afternoon east coast sea breeze pushing inland toward the I- 95 corridor and St. Johns River basin. Thunderstorm hazards include lightning, gusty winds and locally heavy rainfall.

FOG POTENTIAL AND OTHER REMARKS: Late night and early morning patchy fog are possible, especially where recent heavy rainfall occurred. Gusty and erratic winds will occur near thunderstorms.

HYDROLOGY

Due to substantial rainfall across portions of Southeast GA over the last 4 days, area rivers have begun to trend upward in response to the runoff. The Satilla River gauge at Atkinson is projected to rise to Action Stage by Tuesday morning and then reach Minor Flood Stage in the early morning hours Wednesday. While not projected to reach flood stage, the Altamaha will also see rises over the next couple of days. Additional heavy rainfall across the Altamaha basin may nudge the forecast up slightly but it is forecast to crest at Action Stage Wednesday morning followed by decreasing water levels.

PRELIMINARY POINT TEMPS/POPS

AMG 92 74 91 73 / 40 20 30 10 SSI 92 77 95 77 / 40 20 30 20 JAX 94 75 97 77 / 40 20 20 30 SGJ 94 76 97 77 / 40 20 20 20 GNV 94 75 95 76 / 30 10 10 10 OCF 94 74 95 77 / 20 10 10 10

JAX WATCHES/WARNINGS/ADVISORIES

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