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

- Daily Afternoon & Evening Thunderstorms.

- Building heat risk next week potential heat advisory conditions

- Moderate Rip Current Risk Beaches Today

UPDATE

Heat Advisory was cancelled early along the coast as showers and storms cooled the temperatures enough to drop below criteria levels. Lingering showers over the area will continue to push off towards the Atlantic over the next couple of hours. Could see some patchy fog develop close to the dawn hours on Monday morning for those locations which received rain earlier this afternoon.

NEAR TERM /THROUGH TONIGHT/

Main Highlights:

- Peak Heat Indices around 105-109 near the I-95 corridor - Marginal Flood risk due to slow-moving downpours with PM T'Storms for coastal areas of NE FL - Moderate Rip Current Risk Today

Scattered to numerous thunderstorms will begin to develop through the afternoon hours, generally moving southwest to northeast around 10 mph. The slightly stronger southwesterly flow has injected high- grade moisture (PWATs 2"+) into the NE FL that will nourish convection this afternoon while the Atlantic sea breeze stays pinned a few miles from the Atlantic shoreline.

Though storm motion has increased over the last 24 hours, the slow- moving pulses developing along the the sea breeze collision and outflow/storm mergers will be capable of high-volume rain rates for short durations, increasing a localized flood threat mainly for NE FL. To underscore the flood threat today, the Weather Prediction Center has highlighted a sliver of NE FL coast (south of St Augustine) for a Marginal Risk of flooding this afternoon, especially in locations that received significant downpours yesterday. In addition to the flood threat, stronger pulse storms along the sea breeze merger around 4-7 PM today will be capable of gusty winds up to 50 mph and localized episodes of frequent lightning.

Latest surface observations in the eastern/coastal counties are already showing temperatures trending 2-4 degrees warmer than this time yesterday. Heat will build more early this afternoon ahead of convection and combine with dewpoints in the mid/upper 70s, bolstering Heat Index values into the upper 100s, especially in the beachside communities. A Heat Advisory is in effect through 7 PM for the coastal counties and the St Johns River valley, but likely will be potentially ended early as convection ensues during the mid afternoon rain-cools the advised area.

This evening and overnight, thunderstorm activity will move into the adjacent Atlantic waters before sunset with lingering activity over land dissipating through 9 PM. Leftover cloud cover will gradually clear overnight, which may lead to patchy ground fog by dawn Monday, especially in areas where downpours occur this afternoon. Lows tonight will be similarly mild to this morning, reading around the mid 70s inland and upper 70s to near 80 at the coast.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/

Monday and Tuesday...

Main Highlights This Period:

- Daily Max Heat Indices 105-110, Heat Advisory Potential - Daily Mainly Afternoon & Early Evening Storms

Southwest to west steering flow of 10-15 kts continues each day between high pressure extending across south Florida and an approaching trough northwest of the region. Showers and isolated thunderstorms will follow a general diurnal west coast sea breeze regime pattern with morning convection nosing inland from the Suwannee River Valley, then convection expanding inland and eastward into the afternoon as instability increases. The highest daily rain chances focus near and east of the St. Johns River basin to the Atlantic coast mid afternoon into the early evening where the east coast sea breeze, river breeze and boundary mergers focus. Tuesday, the approaching front across southeast GA will bring higher moisture and thus higher rain chances Tuesday afternoon into the evening compared to Monday. The main storm hazards each day will be localized, briefly flooding rainfall and gusty wet downbursts.

Temperatures will continue above average with highs in the mid/upper 90s and daily heat index values right near local Heat Advisory criteria of 105-110 deg, with the higher values across the St. Johns River basin of northeast FL and toward the Atlantic coast given southwest flow. Muggy overnight lows range in the mid/upper 70s inland to near 80 coast.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Wednesday through Saturday...

Main Highlights This Period:

- Above Average Temperatures with High Heat Index Values - Daily Thunderstorm Chances

Major to extreme heat risk mid to late week as high temperatures climb into the upper 90s with heat index values most likely reaching local heat advisory criteria of 108-112 degF at least across portions of northeast FL near the St. Johns River basin toward the Atlantic coast under continued southwest flow. The mid level ridge across south Florida noses northward across north FL Wednesday and dominates through Saturday, which will bring our own regional version of a 'heat dome' and lower than average daily rain chances given subsidence aloft. Rain chances will be higher toward the Atlantic coast each afternoon and evening as well as across southeast GA during the afternoon and into the evening where frontal moisture lingers with rain chances 20-40%.

AVIATION /00Z MONDAY THROUGH 00Z TUESDAY/

Light winds during the overnight hours could allow for shallow fog to develop near inland airfields by sunrise Monday. Breezy southwest winds will lead to early showers once again, as early as 14z will develop with possible BKN cumulus around 2-2.5 kft. Storms will once again develop along the sea breeze and diurnal heating beginning around 18Z/19Z.

MARINE

High pressure ridge will build across central and south Florida early this week as low pressure troughing develops to the north. This pattern will lead to prolonged southwesterly flow during the day followed by nightly surges from the south to Small Craft Exercise Caution speeds. The offshore flow will increase afternoon and evening thunderstorm chances over the local nearshore waters this afternoon and again each day through the upcoming week.

Rip Currents:

Surf between 1 to 3 feet with weak onshore swell will keep rip current risk at low-end moderate levels during the afternoon hours as the sea breeze develops through the first half of the week.

FIRE WEATHER

Southwest flow continue Monday and Tuesday with showers and isolated storms moving inland from the Gulf Coast during the morning, spreading toward the Atlantic coast into the afternoon. The east coast sea breeze will develop and drift inland toward the I-95 corridor mid to late afternoon each day. The best chance of afternoon and evening storms each day will focus between Highway 301 and the Atlantic coast and across inland southeast GA Tuesday afternoon and evening ahead of a stalling front. Dispersion will be elevated across inland southeast GA and parts of the Osceola NF each afternoon. Daily heat index values will approach 105-110 deg. Afternoon minimum humidity will continue above critical values.

Fog Potential and other remarks: Patchy inland fog each morning around sunrise is possible, especially where rainfall recently occurred. Thunderstorms will be capable of producing lightning, torrential rainfall, and erratic wind gusts during the afternoon and evening.

HYDROLOGY

Satilla River at Atkinson will remain in Minor Flood through the Sunday and is forecast to lower into action stage Monday morning.

PRELIMINARY POINT TEMPS/POPS

AMG 76 95 76 95 / 30 30 30 30 SSI 79 94 79 95 / 30 30 10 30 JAX 77 95 77 96 / 10 40 10 30 SGJ 77 94 77 95 / 10 40 10 30 GNV 75 93 75 94 / 10 30 10 20 OCF 76 93 75 93 / 10 30 10 20

JAX WATCHES/WARNINGS/ADVISORIES

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