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 this Week. Heat Advisory Area- Wide from 11 AM 8 PM on Sunday. Heat Advisories & Extreme Heat Warnings Possible Monday through Thursday

- A Few Strong Thunderstorms Possible Late this Afternoon & Evening. Main Impact Area: Inland Southeast GA and the Interstate 10 Corridor. Strong Storm Hazards: Wind Gusts of 35 - 45 mph, Frequent Lightning Strikes,

- Scattered to Numerous Afternoon & Evening TStorms from Mon Sat. Strong to Isolated Severe Storms are Possible Each Day, Mainly Along the I-95

NEAR TERM /THROUGH TONIGHT/

Main Highlights through Tonight:

- Heat Advisory Conditions Continue Area-Wide Today. - Scattered to Numerous Thunderstorms late this Afternoon and Evening, Mainly Across Southeast GA and the Interstate 10 Corridor.

Overnight surface analysis depicts weakening high pressure (1021 millibars) extending from the FL peninsula northwestward along the northern Gulf coast. Meanwhile, a wavy frontal boundary extends from the Carolinas northwestward across the southern Appalachians, the Ohio Valley and the Missouri Valley. Aloft..."Heat Wave" ridging remains centered over the lower Mississippi Valley and eastern Texas, with this ridge extending its axis eastward across the southeastern states. Latest GOES-East derived Total Precipitable Water imagery indicates that seasonably moist conditions prevail across our area, with PWATs generally in the 1.8 - 2.1 inch range. Cirrus cloud cover leftover from evening convection across central and southern GA was drifting across southeast GA, while fair skies prevail elsewhere. Less rainfall coverage across our area on Saturday afternoon and evening has allowed temperatures to run warmer overnight, with values at 07Z still in the upper 70s and lower 80s, with dewpoints generally in the mid to upper 70s.

"Heat Wave" ridging positioned over the lower Mississippi Valley and eastern Texas will begin to slowly retrograde westward later today, allowing for a subtle low level trough to push southeastward across southeast GA late this afternoon and evening. Deep-layered moisture will pool along this trough axis, with PWATs climbing up to near 2.25 inches across southeast GA late this afternoon. Meanwhile, surface ridging will continue to slowly weaken over the FL peninsula and the central / eastern Gulf, with low level westerly flow this morning veering to northwesterly by this afternoon and evening. Strong subsidence this morning should weaken by late this afternoon and early this evening as ridging aloft begins to retrograde further away from our area, and convection should develop along the low level trough axis across mainly inland portions of southeast GA by late this afternoon. There should be enough moisture in place for at least isolated thunderstorms to develop along the Atlantic and Gulf sea breezes by late afternoon, and convective outflows should allow at least scattered convection to drift southward towards the I-10 corridor early this evening. Storms may pulse and become strong as mesoscale boundaries collide, mainly for locations along and north of I-10 through the mid-evening hours before activity dissipates. Stronger storms late this afternoon and evening may produce downburst winds of 35-45 mph, frequent lightning strikes, and locally heavy downpours.

Strong subsidence this morning beneath filtered sunshine due to thin cirrus cloud cover will again allow highs to soar to the mid and upper 90s by the mid to late afternoon hours. Dewpoints may again mix down to the low and mid 70s, yielding peak heat index values in the 108-112 degree range nearly area-wide, which means another day of Heat Advisory conditions, with the onset of advisory criteria beginning as soon as 11 AM this morning and continuing until 8 PM this evening, especially at locations that remain rain-free later today. Convection over southeast GA and northeast FL will dissipate before midnight tonight, with debris cloud cover then gradually thinning overnight through the predawn hours on Monday. Lows will again only fall to the 75-80 degree range by early Monday morning.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/

Main Highlights This Period:

- Isolated Strong to Severe Storms Monday & Tuesday Afternoon/Evening, Especially for Northeast FL

- Heat Index Values Near or Above Heat Advisory Each Day

Surface frontal boundary will drop southward throughout the day on Monday, though lose forward progress rather quickly as it runs into persistent high pressure ridging in the upper levels. Between the overall timing and drier air that tries to fill in behind the boundary, overall best chances for showers and thunderstorms Monday, and likely Tuesday as well, will be across NE FL as well as near the Atlantic sea breeze up the I-95 corridor and coast. Given the presence of some drier air aloft and high late summer instability with above normal temps (more on that below), some isolated strong to severe updrafts will certainly be possible, with downburst winds being the primary threat in addition to torrential rainfall/minor flooding potential.

Though guidance has backed off a bit for the start of the work week, still expecting temps to climb into the mid to upper 90s both Tuesday and Wednesday. Combined with August humidity, Heat Advisories will be likely for at least a portion of the region both days, with Extreme Heat products not our of the realm of possibility.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

Main Highlights This Period:

- Hazardous Heat Continues Mid Week

- Isolated to scattered thunderstorms each afternoon and evening, some which could become strong

Prevailing flow continue from out of the west and northwest through the end of the week as the above mentioned frontal boundary settles just north of the region for mid to late week. Available moisture overall increases later this week with several waves passing along the boundary, and therefore chances for showers and t'storms will overall be on a upward trend for all during the long term period as ridging aloft weakens. This will also slowly drop temperatures closer to normal, though Wednesday and possibly Thursday could still see the hotter temperatures and heat headlines hanging on before this occurs.

AVIATION /12Z SUNDAY THROUGH 12Z MONDAY/

VFR conditions will prevail at the regional terminals through at least 19Z. Showers and thunderstorms developing over interior southeast GA during the early to mid afternoon hours will expand southeastward towards the terminals during the mid to late afternoon hours. However, confidence in coverage and timing remains too low to indicate anything other than vicinity thunderstorm coverage after 19Z, with activity possibly not progressing as far south as north central FL, where we only indicated vicinity showers at GNV after 21Z. Convection should diminish by 03Z Monday, with VFR conditions then expected to prevail at the regional terminals. The Atlantic sea breeze boundary will develop towards noon at coastal locations and will progress inland during the afternoon hours, resulting in surface winds shifting to east-southeasterly around 10 knots at SGJ and southeasterly around 10 knots at SSI before 18Z. Light southwesterly surface winds will diminish to around or less than 5 knots after 02Z. Fog chances still remain too low to include for the overnight hours late Sunday night.

MARINE

Atlantic high pressure will continue to extend its axis westward across the Florida peninsula today, creating a prevailing westerly wind pattern across our local waters. Winds will become onshore across the near shore waters early this afternoon as the sea breeze progresses slowly inland. Southerly winds will then surge this evening, but speeds should remain below Caution levels. Isolated to widely scattered late afternoon and evening thunderstorms will be possible today, mainly for the waters north of St. Augustine. A frontal boundary will then push into the southeastern states by Monday afternoon, with this feature stalling just north of the Georgia waters by midweek. Chances for mainly afternoon and evening showers and thunderstorms will increase across our local waters during the work week. Southwest to westerly winds will continue to prevail, with a westerly evening wind surge forecast on Monday that may bring speeds briefly up to Caution levels.

Rip Currents: A lower end moderate risk is expected today at area beaches as the afternoon sea breeze creates an onshore breeze that will combine with the outgoing tide and a persistent long period east-southeasterly ocean swell. Prevailing offshore winds will strengthen on Monday and Tuesday, creating a low risk that will likely continue through the end of the work week at all area beaches.

FIRE WEATHER

- Heat Advisory In Effect Today - Patchy High Dispersions Inland Southeast Ga Monday And Tuesday

Hot conditions are expected to persist through the rest of the weekend and into at least the start of next week, with Heat Advisories likely and possibly even Extreme Heat Warnings possible each day for most or all of the region. This will come with a flow direction generally out of the southwest to west through the next several days except for a wind shift with the sea breeze generally east of the I-95 corridor. A frontal boundary dropping southward tonight and Monday will return more "usual" chances for showers and storms for all today, then mainly over northeast Florida for early to mid week as some drier air moves into southeast GA behind the front. Better mixing and transport winds will result in good to patchy high dispersions over inland GA, with fair to good dispersions elsewhere. The front will linger just north of the region by late week, with shower and storm chances generally increasing as well.

Fog Potential: Significant fog developments are not expected, however late-night or early-morning fog developments are expected to be shallow and patchy, mainly occurring over areas that have received locally heavy rainfall. Gusty and erratic winds are often possible within and nearby any stronger showers or storms.

CLIMATE

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

Sunday, August 16: KJAX: 97/1957 KGNV: 97/1918 KAMG: 100/1995 KCRG: 95/2022

Monday, August 17: KJAX: 99/1954 KGNV: 97/1954 KAMG: 104/1995 KCRG: 97/2005

Tuesday, August 18: KJAX: 98/1954 KGNV: 98/1954 KAMG: 105/1995 KCRG: 96/2023

PRELIMINARY POINT TEMPS/POPS

AMG 96 76 99 78 / 40 30 20 10 SSI 93 79 95 79 / 60 40 30 10 JAX 96 77 97 77 / 50 40 40 10 SGJ 96 77 96 78 / 30 30 50 10 GNV 96 76 95 77 / 30 20 60 20 OCF 96 75 95 77 / 20 10 50 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 GAZ132>136-149-151>154-162-163-165-166-250-264-350- 364. MARINE...None.