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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

- Widely Scattered Late Afternoon & Evening Thunderstorms Expected for North Central and Inland Northeast FL Today.

- Dangerously Hot & Humid Area-Wide through Monday. Heat Advisory Conditions this Afternoon for Glynn County, GA. Heat Advisories Possible Across Much of Our Area on Monday Afternoon.

- Scattered to Numerous Afternoon and Evening Thunderstorms on Monday and Tuesday, with Strong to Isolated Severe Storm Potential. - Low Potential for Slow Tropical Development off the Southeast U.S. Coast Towards Midweek.

NEAR TERM /THROUGH TONIGHT/

Main Highlights Today and Tonight:

- Widely Scattered Afternoon & Evening Thunderstorms Expected for North Central and Inland Northeast FL this Afternoon and Evening.

- Dangerously Hot & Humid Area-Wide through Monday. Heat Advisory Conditions this Afternoon for Glynn County, GA.

Afternoon surface analysis depicts Atlantic high pressure centered east of Bermuda, with this feature extending its axis westward across the FL peninsula and into the eastern Gulf. Meanwhile, a frontal boundary stretches across the Ohio Valley and the Mid- Atlantic states. Aloft...ridging over the lower Mississippi Valley was extending its axis across our area and southeastward across the Bahamas. Latest GOES-East derived Total Precipitable Water imagery depicts a slightly drier air mass advecting into inland portions of southeast GA, where PWATS were falling to around 1.75 inches, which is just below climatology for late June. Deeper moisture remains in place across the rest of our area, where PWATs were generally around 2 inches. Strengthening subsidence and the slightly drier air mass was suppressing the cumulus field across much of southeast GA and northern portions of the Suwannee Valley, with convection so far relegated to the developing Gulf coast sea breeze along the FL Big Bend / Nature Coasts. Temperatures at 18Z were generally in the 90- 95 degree range at inland locations, while values along the immediate coast in northeast FL have cooled to the upper 80s as an onshore breeze has developed in the wake of the Atlantic sea breeze. Dewpoints at inland locations have generally fallen to the lower 70s, while values have risen to the upper 70s for coastal northeast FL. Heat indices at 18Z were mostly in the 100-105 range across our area.

Ridging aloft will consolidate over the lower Mississippi Valley buy this evening, with this feature steering a shortwave trough eastward across the Ohio Valley and the southern Appalachians tonight, with this feature then pivoting southeastward as it progresses offshore on Monday. A slightly drier and more subsident air mass currently in place over southeast GA and northern portions of the Suwannee Valley will suppress convection this afternoon and evening, and high temperatures will soar to the mid and upper 90s beneath a rather flat cumulus field. Deeper moisture in place over the rest of northeast and north central FL should allow for isolated to widely scattered convection to develop later this afternoon as the Gulf and Atlantic sea breeze boundaries progress inland and interact with other mesoscale boundaries such as the St. Johns River breeze, with slow moving activity tending to cluster around the U.S. Highways 17 and 301 corridors. Convection will likely not materialized until later this afternoon, allowing highs to climb to the mid and upper 90s. Heat indices will peak just below Heat Advisory criteria for most locations, with values generally in the 103-107 degree range, while Heat Advisory conditions still may materialize in Glynn County, where values may peak out around 108.

Convection may linger into the early evening hours across portions of north central and inland northeast FL, with fair skies otherwise prevailing until the predawn hours. The aforementioned shortwave moving across the southern Appalachians overnight will likely push a Mesoscale Convective System (MCS) offshore of the Outer Banks towards sunrise, with a line of convection possibly trailing on the southern end of this MCS near the Savannah River Valley. We have placed isolated POPs across the Altamaha River basin during the predawn hours on Monday in the event that activity extends further southwestward than a majority of the overnight guidance indicates. This MCS will develop along a southward moving "backdoor" cold front, and low level westerly flow should keep lows in the mid to upper 70s at most locations tonight.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/

Main Highlights This Period:

- Numerous Storms on Monday with Scattered Strong Storms Possible.

- Heat Advisory Conditions Possible for Portions of Our Area Monday Afternoon, with Heat Index Values Peaking in the 105-110 Range.

The main weather highlights early this week continue to be the dangerous afternoon heat along with afternoon convection, especially Monday.

On Monday, a large, amplified upper ridging centered to the northwest will keep the door open for a "ridge riding" impulse to drop south into northeast FL. Added forcing from the short wave impulse and corresponding surface trough will combine with convergence along the Atlantic and Gulf sea breezes. There's some uncertainty when t'storms will initiate. At the earliest showers may develop by 10 AM with t'storms possibly beginning around noon. Scattered to numerous storms are expected during the afternoon as outflow interactions persist along the surface trough with highest coverage expected to be focused across NE FL. The main concerns will be gusty winds as initial period of convection will develop in an environment with steep low level lapse rates. It's possible that amid the outflow mergers that a few storms become very strong and possibly severe during the afternoon hours. A second rough of storms may develop during the evening hours as remnant MCS outflow from the north pushes into SE GA, with lingering shower activity fading around midnight.

By Tuesday, steering flow will strengthen as it turns northeasterly, sending more seasonable deep moisture into the area. The faster flow will favor a stronger Atlantic sea breeze and keep the Gulf breeze pinned, resulting in the primary corridor of t'storms to occur along or west of I-75 corridor in NE FL.

Maximum heat indices Monday will approach Heat Advisory conditions, at 105-110 degrees over portions of northeast FL, timing of thunderstorms will heavily impact whether or not locations meet that criteria. Cooling onshore flow and cloud cover will limit heating Tuesday, keeping peak heat indices will be below heat advisory levels, generally in the lower in the 100-105 degree range.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Main Highlights This Period:

- Typical Heat becomes Seasonably Hot Again by Independence Day.

- Lower than Normal Rain Chances Late This Week.

From Wednesday to Friday, weak surface troughing will slide south gradually while ridging aloft builds eastward toward the Mid Atlantic coast, setting up a deep layer easterly flow. The weak trough will extend from FL well into the Atlantic where it may consolidate into a semi-tropical low late in the week but overall confidence is low. Currently, the National Hurricane has maintained a 20% chance of tropical development with the feature. The upper wave over the trough will move toward the area in the easterlies during the Thursday to Friday window, potentially increasing chances for rain and strong thunderstorms. Increasing moisture will support increasing afternoon thunderstorm coverage over the holiday weekend.

Rainfall prospects fall below climo during the second half of the week as drier air in the mid level pushes over the area. That said, there will be daily chances for scattered showers and isolated storms over NE FL. Prevailing easterly flow on Wednesday and Thursday should keep temperatures close to seasonal averages, but above average temperatures appear likely towards Friday and the July 4th weekend as easterly flow weakens due to the break down of the upper ridge.

AVIATION /18Z SUNDAY THROUGH 18Z MONDAY/

VFR conditions will prevail through at least 19Z. Isolated showers may develop after 19Z near SGJ as the Atlantic sea breeze boundary begins to shift inland, but confidence was only high enough for vicinity shower activity this afternoon at SGJ and the Duval County terminals. Confidence was high enough to maintain a PROB30 group for thunderstorms with brief wind gusts up to 30 knots and MVFR visibilities during potential heavier downpours after 20Z through around 01Z Monday. Shower activity could linger at GNV after 01Z, but VFR conditions should otherwise prevail at the regional terminals. Periods of IFR visibilities are expected at VQQ after 07Z. Overnight showers and thunderstorms developing over northern and central GA tonight may shift southeastward towards the SSI terminal during the predawn hours. Confidence was only high enough to include vicinity shower activity at SSI at this time. Southwest to westerly surface winds sustained at 5-10 knots at the Duval County terminals will shift to southeasterly around 10 knots as the Atlantic sea breeze boundary progresses inland this afternoon. Easterly surface winds sustained around 10 knots at SGJ and south-southeasterly winds around 10 knots at SSI in the wake of this seabreeze boundary will continue through around 23Z, followed by surface winds shifting to southerly by 00Z and southwesterly after 06Z. Northwesterly surface winds will then become sustained at the regional terminals after 14Z Monday.

MARINE

Atlantic high pressure centered near Bermuda will continue to extend its axis across the Florida peninsula today, maintaining a prevailing westerly wind flow through the early afternoon hours. Winds will shift to southeasterly this afternoon as the Atlantic sea breeze moves onshore. Southerly winds then increase to Caution levels early this evening across the Georgia waters, followed by winds shifting to southwesterly with gradually diminishing speeds after midnight tonight. A frontal boundary will then approach the Georgia waters from the north on Monday afternoon and evening, with this boundary then stalling over the northeast waters on Tuesday before stalling on Wednesday. Showers and thunderstorms will increase in coverage on Monday and Monday night throughout our local waters, with activity then shifting from the waters adjacent to St. Augustine southward on Tuesday. High pressure wedging down the southeastern seaboard in the wake of this stalling frontal boundary will result in breezy northeasterly winds throughout our local waters on Tuesday and Wednesday, followed by onshore winds gradually diminishing later this week.

Rip Currents:

Breezy onshore winds developing following the passage of the sea breeze later this afternoon will combine with a persistent southeasterly ocean swell to create a lower-end moderate rip current risk at all area beaches. Low surf heights on Monday should drop the risk to low at the southeast GA beaches, with a lower end risk continuing at the northeast FL beaches. Persistent and breezy northeasterly winds on Tuesday and Wednesday should yield a solid moderate risk at all area beaches, with this moderate risk likely continuing through Thursday.

FIRE WEATHER

- Areas Of High Daytime Dispersions Monday And Tuesday

Lower storm coverage this afternoon, mainly south of I-10. Sea breeze from the Gulf and Atlantic will move inland through the afternoon hours and be the focus for thunderstorm activity. Westerly breezes will elevate dispersions across SE GA this afternoon, while lighter flow caps dispersion at fair levels for NE FL. A wind shift to the northwest will accompany a weak trough on Monday. The trough will interact with the sea breezes leading to numerous showers and afternoon Thunderstorms Monday, with strong storms possible. Increasing northeasterly to easterly winds, around 10-15 mph, push in Tuesday, shifting the higher storm and rain chances toward the I- 75 corridor and Big Bend region. Increasing northwesterly transport may result in areas of high dispersion across portions of Monday.

FOG POTENTIAL AND OTHER REMARKS: Significant fog is not expected during the next several days. Stronger storms will be capable of producing strong and erratic wind gusts, along with frequent lightning strikes and heavy downpours, especially on Monday afternoon and evening.

HYDROLOGY

Minor flooding continues along lower portions of the Satilla River Basin, as water levels are currently cresting in a minor flood at the gauge near Atkinson, where minor flooding will continue during the next several days.

PRELIMINARY POINT TEMPS/POPS

AMG 76 96 76 95 / 10 30 30 30 SSI 79 95 80 90 / 10 40 40 10 JAX 76 98 77 93 / 10 50 40 30 SGJ 78 97 77 92 / 10 30 30 40 GNV 76 98 76 95 / 20 30 40 70 OCF 76 95 77 93 / 30 30 20 80

JAX WATCHES/WARNINGS/ADVISORIES

FL...None. GA...Heat Advisory until 5 PM EDT this afternoon for GAZ153-154. MARINE...None.