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

- Dangerously HOT Weather Continues Today. Heat Advisories from 11 AM through 7 PM Today for Locations South and East of Waycross. Heat Advisories are Possible for Portions of Our Area on Friday.

- Scattered to Numerous Afternoon and Evening Thunderstorms Each Day. Main Impact Areas Today: Northeast and North Central FL. Afternoon and Evening Thunderstorm Coverage Increases on Friday and Saturday. Strong to Isolated Severe Storms are Possible During the Afternoon and Evening. Primary Hazards: Wind Gusts of 40-60 mph, Frequent Lightning Strikes, and Torrential, Slow Moving Downpours that Could Create Localized Flooding.

- Afternoon and Evening Thunderstorm Coverage

NEAR TERM /THROUGH TONIGHT/

Highlights through Tonight:

- Near Record High Temperatures Continue Today with Dangerous Heat Indices for Portions of Our Area. Heat Advisories Will Be in Effect from 11 AM through 7 PM Today for Locations South and East of Waycross, GA. - Strong to Isolated Severe Thunderstorms are Possible this Afternoon and Evening Across Northeast and North Central FL. Wet Microburst Potential Will Exist within Stronger Storms, Creating Wind Gusts of 40-60 mph, along with Frequent Lightning Strikes and Localized Flooding.

Early morning surface analysis depicts weak high pressure (1018 millibars) situated over the central Gulf. Meanwhile, a wavy, stationary frontal boundary extends from coastal South Carolina westward across Georgia and the Tennessee Valley, while another frontal boundary was pushing southeastward across the Great Lakes and Missouri Valleys. Aloft...cutoff troughing was spinning over the FL peninsula in between deep-layered Atlantic ridging positioned to the east of the Bahamas and "Heat Wave" ridging centered over the Desert Southwest, with this feature extending its axis eastward across Texas and the lower Mississippi Valley. Otherwise, broad troughing prevails across the Great Lakes and New England. Latest GOES-East derived Total Precipitable Water imagery indicates that an unseasonably dry air mass was persisting across southeast GA, where PWATs have fallen below 1.5 inches. A sharp moisture gradient exists near the FL/GA border, with a tropical air mass remaining in place along and south of the Interstate 10 corridor, where PWATs were around or just above 2 inches. Fair skies now prevail throughout our area, as debris clouds from late evening convection over northeast and north central FL have recently dissipated. Temperatures and dewpoints at 08Z were generally in the 70s across our area.

Cutoff troughing over the FL peninsula will lift slowly northward towards north central and northeast FL by this evening. Slightly cooler temperatures aloft and the presence of tropical moisture should again ignite scattered to numerous showers and thunderstorms this afternoon across northeast and north central FL, while a persistently dry air mass limits convective development for locations north of the Okefenokee Swamp in southeast GA. Convection will likely initiate along the inland moving Gulf sea breeze boundary over the FL Big Bend and Nature coasts towards the early afternoon hours, with activity then expanding northeastward as isolated to widely scattered showers and thunderstorms begin to develop along the inland moving Atlantic sea breeze boundary. Colliding mesoscale boundaries late this afternoon along the U.S. Highways 301 and 17 corridors in northeast and north central FL will allow for convection to "pulse" and become strong or briefly severe, with wet microburst potential continuing due to the tropical air mass and deeply unstable environment. Stronger storms this afternoon and evening will have the potential to produce downburst winds of 40- 60 mph, along with frequent lightning strikes and torrential downpours. Slow storm motion may create localized flooding, especially at urban and low lying, normally flood prone locations.

The bigger story continues to be the unrelenting heat, which will continue today before our weather pattern becomes stormier and slightly cooler during the upcoming weekend. Plenty of sunshine through early this afternoon will boost highs to the 95-100 degree range at most locations, with the drier air mass over southeast GA allowing for dewpoints to crash through the 60s this afternoon. This dry air mass and less cloud cover will likely allow a few interior locations across southeast GA to climb just above 100 degrees this afternoon, but falling humidity values should keep peak heat indices below 108 degrees for locations from Waycross north and westward. Heat indices elsewhere across coastal southeast GA and the Okefenokee Swamp, along with all of northeast and north central FL, will soar to the 108-112 degree range this afternoon.

Convection lingering over inland locations along and south of the I-10 corridor should dissipate towards midnight tonight, with debris cloud cover then thinning out during the overnight and predawn hours on Friday. South to southwesterly low level flow will keep lows in the mid to upper 70s at most locations.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/

Main Highlights This Period (Friday and Saturday):

- Heat advisories may be needed Friday.

- Strong to possibly severe thunderstorms possible Friday and Saturday.

Weak surface low pressure will be centered over the Carolinas this period, with a frontal boundary extending from it across GA. An upper trough will move east into the area Friday afternoon, and be overhead on Saturday. The instability added by this upper trough will result in above average chances for mainly afternoon and evening convection.

Temperatures will be near to a little above average this period.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

Main Highlights This Period (Sunday through Wednesday):

- Strong to possibly severe thunderstorms possible each afternoon and evening.

The weak surface low over the Carolinas will linger this period, with a frontal boundary extending from it across GA. The low level flow will generally be from the southwest, with flow light enough to allow the east coast sea breeze to move inland. Convection will initiate each afternoon due largely to a combination of diurnal instability, and sea breeze interactions.

Near to a little above average temperatures forecast this period.

AVIATION /06Z THURSDAY THROUGH 06Z FRIDAY/

Periods of MVFR visibilities will be possible during the predawn hours at VQQ. Otherwise, VFR conditions will prevail at the regional terminals through at least 17Z. Showers and thunderstorms are expected to develop along sea breeze boundaries on Thursday afternoon, with impacts beginning as early as 18Z at GNV, as convection develops along the inland moving Gulf sea breeze. TEMPO groups were maintained at the Duval County terminals and GNV for brief surface wind gusts around 30 knots and IFR visibilities during heavier downpours through around 01Z Friday. Confidence in impacts is lower at SGJ, where a PROB30 group for brief surface wind gusts around 25 knots and MVFR visibilities during heavier downpours was maintained through around 00Z. Dry weather and VFR conditions will continue to prevail at SSI. Light westerly surface winds sustained around 5 knots or less overnight will shift to northwesterly by 14Z, with sustained speeds increasing to 5-10 knots by 15Z. The Atlantic sea breeze boundary will progress inland after 17Z, shifting surface winds to easterly around 10 knots at SGJ and southeasterly around 10 knots at SSI. This boundary will shift surface winds to southeasterly around 10 knots at CRG and JAX by 21Z. Light southwesterly winds sustained around 5 knots are forecast at the regional terminals following the conclusion of evening convection.

MARINE

Weak high pressure situated over the northern Gulf will maintain a west to southwesterly wind flow across our local waters during the next several days. The Atlantic sea breeze will push slowly inland each afternoon, shifting surface winds to southeasterly and then southerly during the evening hours, with speeds briefly surging to near Caution levels around sunset before diminishing overnight. Meanwhile, a series of frontal boundaries pushing across the southeastern states will stall just north of the Georgia waters through early next week. Scattered showers and thunderstorms may again impact the near shore waters adjacent to northeast Florida this afternoon and evening. Coverage of mainly afternoon and evening showers and thunderstorms will then increase throughout our local waters on Friday and Saturday. Coverage of afternoon and evening thunderstorms will then become more isolated or widely scattered by Sunday and Monday.

Rip Currents: Offshore winds will prevail throughout the morning hours, along with low surf heights, during the next several days. With the outgoing tide occurring later in the afternoon, the overall risk should remain low at area beaches through the upcoming weekend.

FIRE WEATHER

- Patchy high dispersions over Southeast GA this weekend through Monday.

A frontal zone will remain across GA this period. Mainly afternoon and evening thunderstorms are expected each day, with the greatest chances on Friday and Saturday. The potential will exist each day for strong to possibly severe thunderstorms.

Fog Potential: Significant fog formation is not expected. Gusty and erratic winds are expected in and near thunderstorms.

CLIMATE

Near record high temperatures are possible at some of our designated climate sites during the next few days:

Thursday, August the: KJAX: 101/1900 KGNV: 99/1900 KAMG: 104/1995 KCRG: 98/2016

Friday, August 21st: KJAX: 101/1900 KGNV: 99/1983 KAMG: 100/1980 KCRG: 99/2016

PRELIMINARY POINT TEMPS/POPS

AMG 101 75 97 72 / 10 0 70 40 SSI 97 80 93 77 / 10 10 30 30 JAX 98 75 94 74 / 40 20 50 20 SGJ 94 77 94 75 / 40 40 30 10 GNV 95 74 93 73 / 70 50 30 20 OCF 94 74 93 74 / 60 50 50 20

JAX WATCHES/WARNINGS/ADVISORIES

FL...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for FLZ021-023-024-030-031-035-038-120-124-125-132- 136>138-140-220-225-232-233-236-237-240-322-325-333-340- 422-425-433-522-533-633. GA...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for GAZ153-154-162-163-165-166-264-350-364. MARINE...None.