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

- Dangerous Heat Indices Continue this Weekend. Heat Advisory in Effect Today for Northeast and North Central FL and Portions of Southeast GA. High Temperatures: 95-100. Peak Heat Index Values: 105-110.

- Increasing Coverage of Afternoon and Evening Thunderstorms through Early Next Week. Strong to Isolated Severe Storms and Locally Heavy Downpours are Possible Each Afternoon and Evening. Strong Wind Gusts, Frequent Lightning Strikes, and Small Hail will be Possible Later this Afternoon.

NEAR TERM /THROUGH TONIGHT/

Main Highlights Today and Tonight:

- Heat Advisory for Northeast and North Central FL and Portions of Southeast GA this Afternoon through Early this Evening.

- Scattered to Numerous Afternoon and Early Evening Thunderstorms, Mainly for Locations South and East of Waycross, GA.

- Strong to Isolated Severe Storms are Possible Later Today, with Strong Wind Gusts, Frequent Lightning Strikes, and Small Hail Possible.

Early morning surface analysis depicts Atlantic high pressure (1021 millibars) that was centered to the southeast of Bermuda, with this feature extending its axis westward across the FL peninsula. Meanwhile, a wavy frontal boundary extends from coastal New England westward across the Ohio and Missouri Valleys and through the southern Plains states. Aloft...deep- layered ridging extending from the southwestern Atlantic westward across the Deep South was in the process of splitting as a Tropical Upper Tropospheric Trough (TUTT) was pushing northward across the northwestern Bahamas. Otherwise, a potent shortwave trough was pushing slowly southeastward across upper portions of the Mississippi Valley. Latest GOES-East derived Total Precipitable Water imagery indicates that a Saharan Air Layer (SAL) has overspread our region, with PWATs mostly in the 1.5 - 1.75 inch range. Fair skies prevail throughout our region, with temperatures in the 70s at inland locations, ranging to around 80 along the Atlantic coast. Dewpoints were generally in the upper 60s to lower 70s.

Ridging aloft over our area will weaken today as the aforementioned TUTT feature over the Bahamas continues moving slowly northward off the FL Atlantic coast. Meanwhile, shortwave troughing over the upper Mississippi and Missouri Valleys will continue to slide slowly southeastward towards the Ozarks and the Tennessee Valley. A "col" region will develop over our area as ridges consolidate over the lower Mississippi Valley and the western Atlantic. Otherwise, Atlantic high pressure will continue to extend its axis westward across the FL peninsula, maintaining low level west-southwesterly flow. The SAL layer in place over our region will shift northward over interior southeast GA later this afternoon, allowing PWATs to recover to mid-July climatology by late this afternoon.

The SAL overhead this morning should continue to provide strong subsidence that will suppress cloud development, with plenty of sunshine boosting highs to the 95-100 degree range at inland locations, with enough westerly flow to delay the development of the Atlantic sea breeze boundary until early this afternoon. This will allow highs to soar to the mid 90s at coastal locations, with dewpoints then spiking to the mid and upper 70s as the sea breeze migrates slowly inland by the mid and late afternoon. Heat indices should increase to Advisory levels (108 degrees) at coastal locations as this spike in dewpoints occurs. The subsident SAL layer should mix dewpoints down through the 60s across inland portions of southeast GA, but the inland moving sea breeze boundary could increase dewpoints enough later this afternoon to allow Heat indices to reach criteria to reach Advisory levels for inland locations south and east of Waycross, Blackshear, and Jesup. Heat Advisories include all of northeast and north central FL, although confidence is not as high for inland locations, where dewpoints could also mix down into the 60s before convection develops later this afternoon.

Although there will be little in the way of wind shear today, lingering dry air aloft provided by the retreating SAL will again enhance the downdraft potential as thunderstorms develop along mesoscale boundaries during the mid to late afternoon hours , with activity "pulsing" as mesoscale boundaries collide. Scattered activity will potentially last into the evening hours, especially for locations along and north of I-10, where outflow boundaries progressing northward should ignite additional convection. Strong to isolated severe thunderstorms will be possible across much of our area late this afternoon and early this evening, with downburst winds of 40-60 mph, small hail, and frequent lightning strikes possible within stronger storms. Activity will initially develop along the inland moving Gulf sea breeze boundary over north central FL and southern portions of the Suwannee Valley early this afternoon, with mesoscale boundaries colliding over inland north central and northeast FL, where POPs are likely by late afternoon and early this evening.

Convection will diminish towards midnight for locations north of I-10, with debris cloud cover then gradually thinning out after midnight. Lows tonight will generally fall to the mid 70s inland and the upper 70s at coastal locations as low level west- southwesterly flow continues overnight.

SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/

Main Highlights During This Period:

- Increased Storm Chances Sunday Onward.

Steering flow off the Gulf coupled with an approaching front from the north will increase moisture across the area Sunday and Monday, prompting higher convective chances then we've seen this past week. Westerly surface winds will allow the Gulf sea breeze to push far inland, reaching the Atlantic sea breeze closer to I-95, leaving higher strong storm potential in that region as well as closer to the front across southeast Georgia. Still going to be pretty hot on Sunday, with highs in the mid to upper 90s, with the hottest apparent temperatures near the east coast, where values will approach Heat Advisory criteria.

Monday, shower and storm coverage increases further as the aforementioned front sinks further south into central Georgia. Highest storm chances will again be closer to the front, along and north of I-10, and also along the northeast Florida coast where the sea breezes interact. The primary strong storm threats will be gusty winds and heavy rainfall potentially causing flooding concerns. Again, convection may linger past sunset across southeast Georgia mainly. Temperatures will lower a few degrees Monday, with highs in the lower to mid 90s. Isolated storms may linger after sunset both Sunday and Monday nights closer to where the front is, over southeast Georgia.

LONG TERM /TUESDAY THROUGH FRIDAY/

Main Highlights During This Period:

- High storm chances continue Tuesday.

Numerous showers and storms are forecast again for Tuesday as the front sits near the Florida/Georgia state border, then slowly dissipates through the rest of the week. Most of the area is under a 'Marginal' risk of Excessive Rainfall on Tuesday, after several days of heavy rain there will be a threat of localized flooding, especially near the front and over flood prone areas.

Storm chances are generally lower Wednesday onward as northwesterly steering flow brings in drier air, precipitation chances will be around 20-40%. Temperatures will gradually rise again each day through Friday.

AVIATION /06Z SATURDAY THROUGH 06Z SUNDAY/

VFR conditions will prevail at the regional terminals through at least 19Z. Showers and thunderstorms will begin developing near the terminals after 20Z, and we have included PROB30 groups through around 02Z Sunday for brief wind gusts up to 35 knots and IFR to MVFR visibilities during heavier downpours at each terminal. Confidence was a little too low to include prevailing vicinity thunderstorms at SGJ during this time frame, while prevailing VCTS are expected elsewhere. Stronger wind gusts and possibly small hail will be possible after 21Z at the regional terminals, and TEMPO groups will likely be added in future TAF issuances as timing and confidence in coverage and intensity increases. VFR conditions will then prevail at the regional terminals by 04Z Sunday. Southwest to westerly surface winds will remain sustained around 5 knots at the regional terminals through around 14Z, followed by surface winds shifting to northwesterly at 5-10 knots by 15Z. The Atlantic and Gulf sea breezes will move inland on Saturday afternoon, shifting surface winds to southeasterly at 10-15 knots at SGJ towards 18Z and southerly at 10-15 knots at SSI towards 19Z. Outside of developing thunderstorm activity, surface winds at GNV will shift to southwesterly at 5-10 knots towards 20Z, while surface winds elsewhere at the Duval County terminals will generally become southerly around 10 knots towards 20Z. Surface winds will then shift to southwesterly towards 03Z Sunday at the regional terminals, with sustained speeds remaining around 10 knots at the SSI and SGJ coastal terminals and around 5 knots at the inland terminals.

MARINE

Atlantic high pressure will continue to extend its axis westward across the Florida peninsula this weekend, maintaining a prevailing west southwesterly wind flow during the overnight and morning hours, with southeast and southerly winds then 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 may impact the near shore waters late this afternoon and early this evening, possibly containing strong wind gusts, hail, and frequent lightning strikes. Troughing developing over the southeastern states late Sunday and early next week will create a lighter southwesterly wind flow, with numerous mainly afternoon and evening thunderstorms forecast through Tuesday as a frontal boundary sinks into the southeastern states. This feature will likely stall over the southeast Georgia waters before weakening towards midweek. Coverage of showers and thunderstorms will then decrease by Wednesday and especially on Thursday and Friday as the frontal boundary dissipates.

Rip Currents:

Southeasterly winds strengthening late this afternoon will 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 weekend and early next week. Surf heights of less than 2 feet at the northeast FL beaches on Sunday and early next week should also yield a low risk.

FIRE WEATHER

- Areas Of High Dispersions Today And Sunday North Of I-10.

Drier than normal conditions are forecast through Saturday before rain chances begin to increase late weekend and into early next week as a frontal boundary approaches from the north. Southwesterly surface winds continue through Sunday, with areas of high afternoon dispersion along and north of I-10. Despite drier air in place, minRH will remain just above critical values, in the 30 to 40% range away from the coast. Heavy rain potential Sunday through Tuesday as we expected numerous showers and storms each afternoon and evening.

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.

CLIMATE

Daily record high temperatures at our designated climate sites for this weekend, July 11th-12th.

July 11th: KJAX: 104/1879 KGNV: 100/1900 KAMG: 100/1980 KCRG: 99/1998

July 12th: KJAX: 102/1879 KGNV: 99/1902 KAMG: 102/1966 KCRG: 99/2015

PRELIMINARY POINT TEMPS/POPS

AMG 97 75 96 74 / 10 10 40 60 SSI 96 79 97 78 / 30 30 40 40 JAX 98 76 97 76 / 50 30 60 40 SGJ 94 77 95 77 / 30 20 60 20 GNV 97 74 95 75 / 50 30 40 10 OCF 97 74 94 76 / 40 40 30 10

JAX WATCHES/WARNINGS/ADVISORIES

FL...Heat Advisory from noon today 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 noon today to 7 PM EDT this evening for GAZ152>154-162-163-165-166-264-350-364. MARINE...None.