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 through Thursday. Heat Advisories from 11 AM 8 PM Today for Locations South & East of Waycross. Heat Advisories Likely Again on Thursday & Possible on Friday

- Scattered to Numerous Afternoon & Evening Thunderstorms Each Day. Main Impact Areas through Thursday: Locations South & East of Waycross. Afternoon & Evening TStorm Coverage Increases Friday through Sunday. Strong to Isolated Severe Storms are Possible Each Afternoon & Evening. Primary Hazards: Wind Gusts of 40-60 mph, Frequent Lightning Strikes, and Torrential, Slow Moving Downpours that Could Create Localized Flooding

UPDATE

No major updates needed on the forecast this morning.

Highest probabilities for locations reaching 100 degrees will be near the Altamaha river basin this afternoon. With the drier air present over inland southeast Georgia (PWATs currently around 1.5- 1.75"), apparent temperatures will be closer to actual temperatures in the upper 90s to low 100s, below Heat Advisory criteria. For the rest of the area, south of Waycross and including the GA coast, hazardous heat index values continue, ranging from 108-113 degrees.

Drier air in place over southeast Georgia will limit thunderstorm potential today, whereas northeast Florida will again see scattered to numerous showers and storms later today. Best shot for isolated strong storms will be inland and south of I-10 after 2pm, with plenty of heating/instability expected the primary concerns are going to be wet downbursts and locally heavy downpours.

NEAR TERM /THROUGH TONIGHT/

Main Highlights through Tonight:

- Near Record High Temperatures with Dangerous Heat Indices for Portions of Our Area - Heat Advisories from 11 AM through 8 PM today for Locations South and East of Waycross, GA. - Strong to Isolated Severe Thunderstorms Possible this Afternoon and Evening Across Northeast and North Central FL.

- Wet Microburst Potential within Stronger Storms, Possibly Creating Wind Gusts of 40-60 mph, along with Frequent Lightning Strikes and Localized Flooding.

Early morning surface analysis depicts weak high pressure (1019 millibars) situated over the northern Gulf. Meanwhile, a wavy frontal boundary extends from the coastal Carolinas southwestward across the Deep South and then westward across the lower Mississippi Valley and the Southern Plains. Aloft..."Heat Wave" ridging extends from the Desert Southwest eastward across the Southern Plains and lower Mississippi Valley, while deep troughing over Hudson Bay, Canada continues to gradually dig across the Upper Midwest and Great Lakes states. Latest GOES-East derived Total Precipitable Water imagery indicates that tropical moisture prevails for locations south and east of Waycross in southeast GA, where PWATs were generally in the 2 - 2.2 inch range, while a slightly drier air mass prevails north of Waycross, where PWATs were around 1.75 inches. Debris clouds that were leftover from evening convection on Tuesday were persisting across portions of our area. Temperatures at 08Z were mostly in the 70s, except around 80 at coastal locations, with dewpoints generally in the low to mid 70s.

Northwesterly low and mid level flow will continue today as weak surface ridging remains positioned over the northern Gulf. This flow will gradually advect a drier air mass into interior portions of southeast GA, with PWATs likely falling below 1.5 inches from around Waycross northward. Dry weather is expected today north of Waycross, where plenty of sunshine and dewpoints falling through the 60s this afternoon will result in highs approaching 100. Heat index values should remain just below Heat Advisory criteria (108 degrees) from Waycross northward this afternoon.

Meanwhile, broad troughing developing along the eastern periphery of the "Heat Wave" ridge over the FL peninsula will keep a tropical air mass in place from the Okefenokee Swamp and coastal southeast GA southward, where PWATs will remain near or just above 2 inches. This will foster scattered convective development by mid-afternoon along mesoscale boundaries such as the inland moving Atlantic and Gulf sea breezes, in addition to the Lake George and St. Johns River breezes. Lingering debris cloud cover early this morning will dissipate as the day progresses, with highs soaring to near daily record values this afternoon, or in the 95-100 degree range. Dewpoints in the low or mid 70s will create another day of Heat Advisory conditions for locations south and east of Waycross, where values will peak in the 108-112 degree range before late afternoon convection expands and increases cloud cover across our area.

Convection should expand in coverage and pulse late this afternoon and early this evening from the Okefenokee Swamp southward as mesoscale boundaries and convective outflows collide. Plenty of available instability could create a strong to isolated severe thunderstorms, with wet microburst potential in pulsing storms that could create wind gusts of 40-60 mph, along with frequent lightning strikes and torrential downpours. Stronger storms may consolidate along the I-10 and U.S. Highway 301 corridors in northeast and north central FL towards sunset, and weak steering flow aloft could result in heavy rainfall amounts and the potential for localized flooding, especially at urban and normally flood prone locations. Convection may migrate west of the U.S.-301 corridor towards I-75 during the early to mid evening hours before activity diminishes towards midnight. Thinning debris cloudiness is expected during the overnight and predawn hours on Thursday, with lows in the 70s forecast area-wide.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/

Main Highlights This Period (Thursday and Friday):

- Potential for strong to severe thunderstorms each afternoon

- Heat Advisories may be needed each day

A frontal boundary extending from low pressure over the Carolinas will remain over southern GA this period. An upper trough will be in place over the area this period. The low level flow will be from the southwest, with the east coast sea breeze moving past I95 each afternoon. The combination of diurnal heating, sea breeze convergence and enhanced instability under upper trough will yield above average chances for showers and storms in the afternoon and evening hours this period.

Temperatures will remain above average this period. Heat advisories may be needed each day.

LONG TERM /SATURDAY THROUGH TUESDAY/

Main Highlights This Period (Saturday through Tuesday):

- Strong to severe thunderstorm chances each afternoon and evening

Area of low pressure will remain over the Carolinas throughout this period, with a frontal boundary extending from it across GA. Upper troughing will strengthen early this period, with waves passes through the trough, before moving of to the east Monday. The greatest chance for showers and storms this period will be Saturday.

Temperatures will trend a little above average this period.

AVIATION /12Z WEDNESDAY THROUGH 12Z THURSDAY/

VFR conditions will prevail at the regional terminals through at least 18Z Wednesday. Showers and thunderstorms will begin developing near the northeast FL terminals towards 19Z, with dry weather and VFR conditions expected to prevail at SSI throughout the forecast period. PROB30 groups were maintained from around 20Z through around 01Z at the northeast FL terminals, with higher confidence for IFR visibilities during heavier downpours at GNV and VQQ where TEMPOs are now in place. Brief surface wind gusts around 30 knots are expected during convection at the northeast FL terminals on Wednesday afternoon and evening. Convection near the northeast FL terminals should dissipate by 03Z Thursday, with VFR conditions expected to prevail thereafter other than typical morning visibility restrictions at VQQ.

MARINE

Weak high pressure situated over the northern Gulf will maintain a northwest to westerly wind flow across our local waters today. The Atlantic sea breeze will push slowly inland this afternoon, shifting surface winds to southeasterly this afternoon and then southerly this evening, with speeds briefly surging around sunset before diminishing overnight. Meanwhile, a stalled frontal boundary positioned just north of the Georgia waters will remain in place during the next several days. Scattered showers and thunderstorms may impact the near shore waters adjacent to northeast Florida this afternoon and evening and again on Thursday afternoon and evening. Coverage of mainly afternoon and evening showers and thunderstorms will then increase from Friday through the upcoming weekend throughout our local waters as southwesterly winds prevail, with afternoon sea breezes developing each day.

Rip Currents: Offshore winds and low surf heights will prevail during the morning hours at area beaches during the next several days. However, the afternoon sea breeze will coincide with the outgoing tide during the next few afternoons, with breezy onshore winds likely creating a lower end moderate risk at all area beaches through Friday. Low surf heights and later outgoing tide times this weekend could lower the risk at area beaches.

FIRE WEATHER

- Patchy high dispersions Today

A frontal zone will remain stalled over southern GA this period. Daily rounds of showers and thunderstorms are expected, mainly in the afternoon and evening hours.

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

CLIMATE

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

Wednesday, August 19th: KJAX: 99/1900 KGNV: 100/1954 KAMG: 103/1995 KCRG: 97/2010

Thursday, August 20th: 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 99 74 100 75 / 10 10 10 0 SSI 98 79 95 79 / 20 10 10 0 JAX 98 75 96 76 / 60 20 40 10 SGJ 95 77 95 76 / 40 40 40 10 GNV 94 76 95 75 / 60 40 60 10 OCF 92 76 95 75 / 40 30 70 20

JAX WATCHES/WARNINGS/ADVISORIES

FL...Heat Advisory from 11 AM this morning to 8 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 8 PM EDT this evening for GAZ153-154-162-163-165-166-264-350-364. MARINE...None.