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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

- Dangerous Heat Continues Today. Heat Advisory along the I-95 & U.S.-301 corridors in Northeast FL & Southeast GA. High Temperatures: 93- 99 and Peak Afternoon Heat Index Values: 103- 110

- Strong to Isolated Severe TStorms this Afternoon through Early Evening. Hazards: Damaging Winds of 40-60 mph, Frequent Lightning & Heavy Downpours

- Increasing Coverage of Afternoon Thunderstorms Monday & Tuesday. Heavy Downpours & Localized Flooding Possible

- Heat & Humidity Returns Late this Week and into Next Weekend

NEAR TERM /THROUGH TONIGHT/

Main Highlights Today and Tonight:

- Dangerous Heat Continues Today, with Heat Advisory Conditions Along the I-95 and Most of the U.S. Highway 301 Corridor.

- Scattered to Numerous Afternoon and Early Evening Thunderstorms, with Strong to Isolated Severe Storms Possible. Stronger Storms will be Capable of Producing Damaging Wind Gusts, Frequent Lightning Strikes, and Heavier Downpours Late this Afternoon and Early this Evening.

Early morning surface analysis depicts Atlantic high pressure (1021 millibars) centered to the south of Bermuda, with this feature extending its axis westward across south FL and the southeastern Gulf. Meanwhile, a wavy frontal boundary extends from North Carolina's Outer Banks westward across the southern Appalachians, the Tennessee Valley, the Ozarks and the Southern Plains states. Another high pressure center (1021 millibars) was building over the Great Lakes and New England in the wake of this frontal boundary. Aloft...a shortwave trough was pushing slowly southward from the Ohio Valley towards the Tennessee Valley, with this feature shifting deep-layered ridging centered over the Bahamas slowly southward. Otherwise, "heat wave" ridging was expanding over the Rockies and the Plains states. Latest GOES-East derived Total Precipitable Water imagery indicates that PWAT values continue to slowly increase across our region, with values ranging from 1.6 - 1.9 inches. Mid and high altitude cloudiness was persisting across portions of northeast and north central FL, with fair skies otherwise in place. Isolated convection was already developing along the FL Nature Coast near Cedar Key and Crystal River in the prevailing westerly flow pattern. Temperatures and dewpoints at 08Z were in the 70s area-wide.

Troughing digging slowly southward across the Tennessee Valley and the southern Appalachians will push a frontal boundary southward through the Carolinas today and into northern GA towards sunrise on Monday. Westerly low level flow will gradually deepen downstream of this boundary today and tonight across our area, advecting a plume of tropical moisture from west to east across our region this afternoon and evening, resulting in PWATs rising above 2 inches later today across northeast and north central FL, with tropical moisture then overspreading southeast GA this evening. Although mid- level dry air will be departing our area this afternoon, intense heating this morning and early afternoon beneath mostly sunny skies will likely keep relatively steep lapse rates in place this afternoon, setting the stage for another round of strong to isolated severe storms across our area late this afternoon and early this evening.

Westerly flow will delay the development of the Atlantic sea breeze boundary until the early afternoon hours, driving dangerous heat to coastal locations once again today. Highs will again soar to the mid and upper 90s at most locations before thunderstorm activity increases in coverage and intensity from west to east across northeast and north central FL, with outflow boundaries then advecting northward into southeast GA early this evening, triggering scattered convection. A Heat Advisory that was initially in place for the I-95 and U.S. Highway 17 corridors was expanded inland to include the U.S. Highway 301 corridor across northeast FL and southeast GA, where Heat Index values will peak around the 108 degree threshold. Coastal locations may experience peak heat indices around 110 during the early to mid afternoon hours as the Atlantic sea breeze pushes inland, resulting in dewpoints rising to the mid and upper 70s. Peak heat index values elsewhere should remain in the 100-107 degree range as intense heating allows dewpoints to mix down to around 70 by the mid-afternoon hours.

Isolated convection developing along the FL Nature Coast during the predawn hours could send a few showers towards western portions of Marion County through around sunrise. Otherwise, convection will initially develop along the Gulf coast sea breeze early this afternoon along the FL Big Bend and Nature Coasts, with activity then increasing in coverage and intensity as the Gulf sea breeze boundary progresses eastward. Strong to isolated severe storms will be possible by the mid to late afternoon hours, with activity potentially interacting with a much slower moving Atlantic sea breeze boundary late this afternoon along the I-95 corridor. Mesoscale boundary collisions will again drive storm intensity, with "pulsing" storms potentially creating downburst winds of 40-60 mph, along with frequent lightning strikes and locally heavy downpours. Activity will then spread into southeast GA towards sunset, where activity could linger into the evening hours, while convection over northeast and north central FL pushes eastward over the Atlantic waters. Activity could linger through around midnight for the I-95 corridor and coastal southeast GA before dissipating overnight. Nocturnal convection may be a little more numerous over Apalachee Bay and the FL Big Bend and Nature Coasts during the predawn hours on Monday, with isolated convection potentially pushing into southern portions of the Suwannee Valley and portions of north central FL towards sunrise. Low level westerly flow will keep lows in the low to mid 70s inland and the mid to upper 70s at coastal locations tonight.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/

Main Highlights During This Period:

- Increased Storm Chances Monday and Tuesday - Potential for excessive rainfall and strong storms north of I-10

More widespread diurnal bouts of showers and storms are anticipated for Monday and Tuesday as high pressure ridging extending in over the southern Florida peninsula and as low pressure to the north interact to create a southwesterly-westerly flow through the start of the week bringing increased moisture levels and instability leading to a potential for excessive rainfall and strong to severe storms, especially for areas north of the I-10 corridor. High temperatures for the beginning of the week will rise into the lower to mid 90s with overnight low temperatures dropping down into the lower to mid 70s. Heat index values will are expected to range upwards of above 100, but is likely to remain below Heat Advisory criteria.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

Main Highlights During This Period:

- Reduced chances for storms starting midweek - Heat re-builds into the region through Friday

Convection is expected to be less widespread by midweek as the influence of high pressure ridging extending in from out of the east crosses further over the Florida peninsula and low pressure to the north shifts further to the west, resulting in relatively more stable conditions and drier air overhead. Storm developments are expected to become more widespread by the end of the week and into the weekend as high pressure moves westward into the Gulf and flow shifts to be more out of the northwest with upper level short waves potentially dipping in over the region by the weekend. Above average temperatures, with max temps rising into the mid 90s, will continue through the end of the week with heat index values potentially rising to Heat Advisory levels through the period.

AVIATION /12Z SUNDAY THROUGH 12Z MONDAY/

VFR conditions will prevail at the regional terminals through at least 18Z. Showers and thunderstorms will begin developing along sea breeze boundaries towards 19Z, with potential impacts beginning at GNV before 20Z, followed by activity progressing eastward towards the rest of the northeast FL terminals and SSI, where potential impacts could continue through around 01Z Monday. Enough uncertainty in timing and coverage remains in place for us to maintain PROB30 groups at each terminal during the afternoon and early evening hours, with brief wind gusts up to 35 knots possible, along with IFR visibilities during heavier downpours and brief periods of MVFR ceilings around 3,000 feet. Lingering showers could continue at the SGJ and SSI coastal terminals through around 03Z, but VFR conditions will otherwise prevail after 01Z Monday. Southwesterly surface winds will remain sustained at 5-10 knots through around 14Z at the coastal terminals, with speeds of 5 knots or less at the inland terminals. Surface winds will then shift to west-northwesterly after 14Z, with speeds gradually increasing to around 10 knots at the regional terminals. The Atlantic sea breeze will develop early this afternoon and will move inland, shifting surface winds at SGJ to southeasterly towards 19Z, with speeds increasing to 10-15 knots. Surface winds at SSI will shift to southerly by 20Z, where speeds will also increase to 10-15 knots. Southwesterly surface winds will then remain sustained at 5-10 knots at the regional terminals once convection winds down after 02Z Monday.

MARINE

Atlantic high pressure will continue to extend its axis westward across the Florida peninsula today. Westerly winds will continue this morning, followed by southeasterly and then southerly winds developing and surging to Caution levels during the late afternoon and evening hours as the Atlantic sea breeze shifts inland. A few strong or even severe thunderstorms pushing eastward may impact our local waters late this afternoon and early this evening, possibly containing strong wind gusts and frequent lightning strikes.

A frontal boundary will then sink southward towards the Georgia waters on Monday, with this feature stalling over the Georgia waters on Tuesday before weakening later this week. Showers and thunderstorms may impact our local waters earlier during the afternoon hours on Monday and Tuesday, with a few strong storms possible, especially for the waters north of St. Augustine. Coverage of showers and thunderstorms will then decrease by Wednesday and especially on Thursday and Friday as the frontal boundary dissipates, with only isolated to widely scattered late afternoon and early evening activity possible for the near shore waters as a prevailing westerly flow continues during the overnight and morning hours each day.

Rip Currents:

Southeasterly winds strengthening late this afternoon will again create a lower end moderate risk at the northeast FL beaches, with surf increasing to around 2 feet towards sunset. Lower surf of only 1-2 feet at the southeast GA beaches should yield a low risk throughout the upcoming week. Surf heights of less than 2 feet at the northeast FL beaches should also yield a low risk during the upcoming work week.

FIRE WEATHER

- Areas Of High Dispersions Through Wednesday North Of I-10

High chances for showers and storms today and Monday as instability situated ahead of a frontal boundary approaches from the north. Southwesterly surface winds continue through early next week, with areas of high afternoon dispersion along and north of I-10. Heavy rain potential today through Tuesday due to expected numerous showers and storms each afternoon and evening with winds consistently building in the afternoon from out of the west and southwest through the end of the week.

Fog Potential and other remarks: Significant fog potential is not expected. Erratic wind gusts possible in and near thunderstorms, and at times, at a distance due to outflows.

PRELIMINARY POINT TEMPS/POPS

AMG 98 73 90 72 / 40 40 60 50 SSI 95 76 93 76 / 30 20 70 60 JAX 97 75 94 74 / 70 30 70 40 SGJ 94 76 94 76 / 60 30 60 10 GNV 94 74 93 74 / 70 30 50 20 OCF 93 74 93 76 / 70 10 40 10

JAX WATCHES/WARNINGS/ADVISORIES

FL...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for FLZ023-024-030-031-038-124-125-132-137-138-225-232- 233-237-325-333-425-433-533-633. GA...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for GAZ136-151>154-165-166-264-350-364. MARINE...None.