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 Thunderstorms Expected for North Central and Possibly Coastal Northeast FL this Afternoon.

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

- Isolated strong storm potential across north-central FL this afternoon and evening.

- Hot and humid this afternoon, with heat indices 100-110 F. A Heat Advisory for Glynn County this afternoon, where heat indices will peak around 110 degrees.

Atlantic surface high pressure ridging over the FL peninsula continues westerly flow today as "Heat Wave" ridging aloft centered over the lower MS Valley extends over the SE US. Building subsidence and slightly drier air (PWATs 1.6-1.8 in) filtering in from the northwest will limit convection to north- central FL. Isolated showers and storms develop along the diurnal sea breezes late this morning into early afternoon becoming widely scattered in the late afternoon/early evening as mesoscale boundaries collide mainly south of Gainesville and St. Augustine. An isolated strong storm can't be ruled out. Less convective coverage and associated cloud cover will allow inland temperatures to soar to the mid and upper 90s this afternoon, with prevailing low level westerly flow delaying the development of the Atlantic sea breeze until the mid-afternoon hours, allowing coastal highs to climb to the mid 90s. Heat indices also rise into the 100-107 F range and into Heat Advisory (>= 108 F) range in Glynn County. Meanwhile, a shortwave trough shifts southward down the SE seaboard developing a MCS that weakens as it approaches SE GA later this evening. A few showers may move into SE GA later tonight with this feature. Otherwise, convection in north- central FL should wane after sunset. Overnight lows will be in the mid to upper 70s.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/

Main Highlights This Period:

- Numerous Storms on Monday and Tuesday Afternoons and Evenings, with Strong Storm Potential Along the U.S.-301 and I-95 Corridors.

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

Afternoon and evening thunderstorms are expected both Monday and Tuesday, with hot high temperatures and dangerous maximum afternoon heat indices. On Monday, weak westerly winds will prompt higher thunderstorm activity later in the afternoon closer to I-95, with a switch up on Tuesday as surface winds begin to shift to northeasterly as low pressure develops off the southeast US coast. The northeasterly winds will shift the focus of increased thunderstorm coverage closer to I-75/inland northeast Florida on Tuesday. Strong storms will be possible both days, especially as mesoscale boundaries collide and storms pulse, with downburst winds of 40-55 mph, frequent lightning strikes, and heavy downpours expected within stronger activity.

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. With more cloud cover and an earlier start to convection Tuesday, max heat indices will be slightly lower in the 100-105 degree range.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

Main Highlights This Period:

- Monitoring the Gulf Stream Waters off the Southeastern Seaboard for Potential Tropical Development Towards Midweek

- Daily Thunderstorm Coverage Shifts Southward, Especially by Thursday and Friday.

Weak surface troughing will continue to move slowly southward across our region, with high pressure building over the Mid- Atlantic states wedging down the southeastern seaboard in the wake of this southward moving trough. This evolution of the weather pattern will provide a deepening easterly flow regime across our area, which should provide some relief from the oppressive heat that is forecast on Sunday and Monday. Lower storm chances are expected Wednesday through Saturday, with chances around 20-40%, with morning isolated activity near the northeast Florida coast, then the storm coverage will be focused over inland northeast Florida in the afternoons/evenings. 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.

The National Hurricane continues to maintain a 20% chance of tropical development off the southeastern United States within 7 days, monitor the forecast at hurricanes.gov.

AVIATION /12Z SUNDAY THROUGH 12Z MONDAY/

VFR conditions will prevail through at least 16Z. Isolated showers and possibly a thunderstorm or two could develop after 16Z at the SSI and SGJ coastal terminals as the Atlantic sea breeze boundary begins to shift inland, but confidence was only high enough for vicinity shower activity at these terminals and then at the Duval County terminals after 19Z. 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 between after 20Z. Shower activity could linger at GNV after 00Z, but VFR conditions should otherwise prevail at the regional terminals by 01Z Monday. Periods of IFR visibilities are expected at VQQ after 06Z. Light southwest to westerly surface winds developing by 14Z will generally shift to west northwesterly by 16Z, with sustained speeds increasing to 5-10 knots. The Atlantic sea breeze boundary moving inland this afternoon will shift surface winds to easterly around 10 knots at SGJ towards 17Z and south- southeasterly around 10 knots at SSI by 18Z, with this boundary then crossing the Duval County terminals in the 19Z-22Z range from east to west, shifting surface winds to southeasterly around 10 knots. Surface winds will then shift to southerly at 5-10 knots towards sunset at the regional terminals, with southwesterly winds around 5 knots prevailing at the coastal terminals after 06Z Monday.

MARINE

Atlantic high pressure ridge axis over the FL peninsula will shift southward today. Light southwesterly winds this morning will shift to south-southeasterly this afternoon due to the Atlantic sea breeze shifting onshore. Southerly winds then increase to small craft exercise caution levels later this evening. A weak back door frontal boundary will approach the waters on Monday and stall over the waters Tuesday into Wednesday, supporting increased coverage for showers and thunderstorms for early week.

Rip Currents:

A lower end moderate risk will develop each afternoon at area beaches as onshore winds become breezy following the passage of the sea breeze combined with a southeasterly ocean swell.

FIRE WEATHER

- High Daytime Dispersion Values across Inland Portions of Southeast GA this Afternoon.

Only isolated to widely scattered afternoon and early evening thunderstorms are forecast on Sunday, mainly for locations south of the Interstate 10 corridor. Westerly transport winds will continue on Sunday, with breezy conditions developing across inland southeast GA that will create high daytime dispersion values, while lighter speeds across northeast and north central FL yielding generally fair values. Transport winds will shift to west-northwesterly on Monday, with elevated mixing heights yielding generally good daytime dispersion values for inland locations, with patchy high values near I-10. Numerous afternoon and evening showers and thunderstorms are forecast on Monday, with strong storms possible along the I-95 and U.S. Highway 301 corridors. 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 and Tuesday during the afternoon and evening hours.

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 96 76 96 76 / 0 10 40 40 SSI 94 79 94 80 / 10 0 40 40 JAX 96 77 97 77 / 10 10 40 40 SGJ 94 77 96 78 / 10 10 30 30 GNV 95 75 97 76 / 30 20 30 30 OCF 94 75 96 77 / 30 20 30 20

JAX WATCHES/WARNINGS/ADVISORIES

FL...None. GA...Heat Advisory from noon today to 5 PM EDT this afternoon for GAZ153-154. MARINE...None.