Area Forecast Discussion

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

- Heat and Humidity Builds through Early Next Week. Heat Index Values Rise to the 100-105 Range Inland this Afternoon & Friday. Heat Advisory Conditions Possible this Weekend as Values Rise to 105-110

- Scattered to Numerous Afternoon & Evening TStorms Inland Today. Heavy Downpours & Frequent Lightning Strikes Possible Across North Central FL

- Moderate Rip Current Risk at All Area Beaches this Afternoon

- Afternoon & Evening TStorms Area-Wide this Weekend into Next Week. Strong Storms with Gusty Winds, Frequent Lightning Strikes & Heavy Downpours

- Possible Along the I-95 Corridor

NEAR TERM /THROUGH TONIGHT/

Main Highlights This Period:

- Scattered to numerous showers and thunderstorms this afternoon and evening, mainly for inland locations.

- Heavy downpours and frequent lightning strikes will be possible near the I-75 corridor in north central FL late this afternoon and early this evening.

- Heat index values peak in the 100-105 degree range at inland locations this afternoon as highs climb to the low and mid 90s.

- Moderate rip current risk at all area beaches as breezy onshore winds develop this afternoon.

Early morning surface analysis depicts weakening high pressure (1021 millibars) centered near Bermuda, with this feature extending its axis across our region. Meanwhile, a cold front extends from the western Great Lakes through the Plains states. Aloft...ridging centered over Texas and the lower Mississippi Valley was expanding eastward across the Deep South. Otherwise, troughing was digging from the Rockies and the Northern Plains states eastward towards the Upper Midwest. Latest GOES-East derived Total Precipitable Water imagery indicates that a slightly drier air mass has advected onshore from the Atlantic waters along the Interstate 95 corridor, where PWATs have fallen to the 1.5 - 1.7 inch range. Values at inland locations range from around 1.7 inches for locations near the Altamaha River in southeast GA to near 2 inches across portions of north central FL. A few pockets of stratocumulus cloud cover were developing in the warm and humid air mass that was in place locally, with fair skies prevailing for most locations south of the I-10 corridor. Temperatures at 07Z generally ranged from 70-75 degrees inland, with mid to upper 70s prevailing at coastal locations. Dewpoints were mostly in the upper 60s and lower 70s.

Ridging aloft will expand into our area today, with less cloud cover and rising heights aloft providing summertime heat and humidity to our region this afternoon. Plenty of sunshine this morning will allow highs to soar to the low and mid 90s by the mid to late afternoon hours at inland locations, where heat index values will peak in the 100-105 degree range. The Atlantic sea breeze boundary should develop towards noon at area beaches and will move well inland this afternoon, with breezy southeasterly winds developing by mid-afternoon keeping coastal highs in the upper 80s to near 90.

Weakening Atlantic surface high pressure centered near Bermuda will extend its axis across our region for one more day, providing a prevailing southerly wind flow and keeping a slightly drier air mass in place along the I-95 corridor and points eastward. Enough moisture will remain in place elsewhere for scattered convection to develop along inland moving mesoscale boundaries early this afternoon, with coverage and intensity expected to increase across north central FL late this afternoon as mesoscale boundaries collide. Relatively mild temperatures aloft and poor lapse rates should keep thunderstorm activity tame today, with any storms that pulse likely containing heavy downpours and frequent lightning strikes as their primary threats. Mesoscale boundary collisions could continue across inland southeast GA and between the U.S. Highway 301 corridor and I-75 this evening, with lingering activity expected to dissipate towards midnight at these inland locations. Debris cloud cover should thin out during the overnight and predawn hours on Friday, with muggy conditions otherwise continuing, as lows only fall to the low and mid 70s inland, ranging to the mid and upper 70s at coastal locations.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/

Main Highlights This Period:

- Dangerous Heat for Sensitive Groups This Weekend.

- Scattered to Numerous Thunderstorms Along the Coastal Counties This Weekend.

- Moderate Risk for Rip Currents at Area Beaches on Friday.

Weakening Bermuda High pressure surface ridge axis weakens to the south of the area with light WSW low level flow while mid level ridging aloft strengthens to the west along the Gulf coast into southern TX, deflecting a shortwave trough eastward from the upper Midwest to the eastern Great lakes. This feature will support a cold front moving ESE through the TN valley before stalling across the deep south in the afternoon. Generally above normal moisture levels will be in place (Precipitable Water levels 1.6-1.90 inches) from WNW low/mid level flow. While shortwave energy will be absent, high moisture combined with diurnal heating will support scattered T'storm coverage focused along the US-17/I-95 corridors as the Gulf seabreeze and prevailing WSW flow interacts with the Atlantic seabreeze shifting onshore to I-95. Shear will be light, and warm mid level temperatures likely eliminate severe T'storm potential, through elevated DCAPE values could support some stronger wind gusts to 40 mph.

Saturday, a cold front will stall just north of the area across central/northern GA as another shortwave moves eastward through the OH valley into the Mid Atlantic states, paralleling north of the frontal boundary. Low level WNW flow around the mid level ridge retreating a bit to the western Gulf waters will pump higher moisture levels (PWATS 1.8-2.0 inches) and combined with strong daytime heating and some incoming shortwave energy from the NW will generate scattered T'storms with numerous coverage along I-95 where light WNW winds will interact with Atlantic seabreeze and prompt new T'storms outflows that will elevate coverage. Locally heavy downpours, frequent lightning, and brief wet downburst wind gusts to 40-50 mph are the main hazards due to heavy water loading.

Sunday, the frontal boundary across the deep south will dissipate with westerly light flow around weak high pressure over the eastern Gulf waters. Similar to Saturday, scattered T'storms will develop in the strong diurnal heating and high moisture levels with greatest coverage focused along the I-95 and US-17 corridors during the afternoon.

Heat index values will become increasingly hot friday into the weekend as highs in the mid/upper 90s west of I-95 combined with low 70s dewpoints in the warm moist low level airmass will elevate heat index values to bump up heat index values to 104-108 Friday and 105- 109 Saturday and Sunday, ranging into low end heat advisory criteria as before any T'storms provide rain cooled air.

Lows will remain muggy with mid 70s inland and the upper 70s along the coast. Patchy, shallow ground fog will be limited to locations where locally heavy rainfall occurs.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

Main Highlights This Period:

- Scattered to Numerous Daily T'storms each day next week

- Above normal Temperatures into early next Week with

- Elevated Heat Index Values Through at least Tuesday

The period will will be marked by troughing over the eastern third of the US with ridging aloft ESE of the region. A surface frontal boundary will slowly sink from the mid and lower MS valley Monday into the deep south Tuesday and remain nearly stationary through Wednesday. Southwest low level flow, elevated at the surface due to a tighter pressure gradient between Atlantic high pressure to the southeast and the frontal boundary to the NW, will favor the Gulf seabreeze moving well inland each day before merging with Atlantic seabreeze close to the I-95 corridor.

Above normal moisture, strong diurnal heating, and lift along the seabreezes with create scattered to numerous T'storms each day lingering past sunset before fading by midnight.

Temperatures will begin above normal with increasing clouds and more numerous T'storms bringing high near normal by Wednesday. Elevated Heat Index values 102-106 will continue into Tuesday. Lows will remain above normal during the period.

AVIATION /12Z THURSDAY THROUGH 12Z FRIDAY/

VFR conditions will prevail at the regional terminals through at least 18Z. Showers and thunderstorms will develop along inland moving mesoscale boundaries such as the Gulf and Atlantic sea breezes and the St. Johns River breeze towards 18Z, with activity likely converging and increasing in coverage between the U.S. Highway 301 and Interstate 75 corridors after 20Z. Confidence was only high enough to indicate vicinity showers at the SSI and SGJ coastal terminals as activity initially develops along the Atlantic sea breeze after 16Z, with vicinity showers also indicated at JAX after 17Z. Confidence was high enough to forecast vicinity thunderstorms at GNV and VQQ after 20Z, with a PROB30 group for briefly gusty winds and MVFR conditions during heavier downpours included through 00Z Friday at the GNV terminal. Activity should dissipate by 02Z at GNV, with VFR conditions otherwise prevailing this evening. Light southerly surface winds sustained around 5 knots or less will prevail at the regional terminals through around 14Z, followed by speeds increasing to 5-10 knots by 17Z. Surface winds will then shift to southeasterly at 10-15 knots at the coastal terminals by 19Z.

MARINE

Atlantic high pressure centered near Bermuda will weaken and shift southward later today and tonight. A frontal boundary will then enter the southeastern states on Friday night before stalling to the north of our waters during the weekend. Light southerly winds this morning will become onshore early this afternoon as the Atlantic sea breeze shifts inland, with breezy conditions developing by late this afternoon across the near shore waters. Winds will then shift to southerly early this evening and will surge to near Caution speeds throughout our local waters. Unseasonably dry weather will otherwise continue through Saturday. Prevailing winds will become westerly on Friday morning, followed by breezy southeasterly winds developing by late afternoon. Southerly evening wind surges are forecast this weekend. Scattered afternoon and evening showers and thunderstorms are then expected each afternoon and evening beginning on Sunday, with some potential for stronger storms across the Georgia waters early next week as another frontal boundary pushes into the southeastern states.

Rip Currents: A lower end moderate risk will continue today at area beaches, especially this afternoon as developing onshore winds combine with a lingering longer period northeasterly ocean swell. This swell will likely fade by on Friday, with low surf heights expected to lower the risk at the southeast GA beaches through the weekend. A lower end moderate risk may continue this weekend at the northeast FL beaches, mainly during the late afternoon hours as winds become south-southeasterly following the inland movement of the sea breeze.

FIRE WEATHER

- Areas Of High Dispersions On Sunday

Bermuda High Pressure will extend across the area today with light southerly winds turning southeasterly behind the Atlantic seabreeze and scattered showers and isolated T'storms developing inland between the I-95 and I-75 corridors with more numerous showers over north central FL. Friday, south to southwesterly winds will keep Atlantic seabreeze pinned near US-17 with scattered T'storms in the afternoon over eastern zones. Higher moisture will arrive this weekend with scattered to numerous afternoon T'storms focused east of highway 301 as the Atlantic seabreeze remains pinned to the east of I-95. Light south to southwesterly transport winds will keep dispersion levels in the fair to good range today into Saturday with increasing transport winds on Sunday creating areas of high dispersions. FOG POTENTIAL AND OTHER REMARKS: Patchy inland fog is possible but significant fog development is not expected.

CLIMATE

The return of summertime heat later this week and over the weekend will lead to near record temperatures. Less likely to see readings reach record highs but there is potential for record high minimum temperatures to be threatened.

Record High Temperatures:

June 12: KJAX: 99/1998

June 13: KJAX: 100/1977

Record High Minimum Temperatures:

June 11: KJAX: 77/2005 KGNV: 75/2005

June 12: KJAX: 79/1952 KGNV: 76/1963

June 13: KJAX: 79/1880 KGNV: 79/1998

June 14: KJAX: 79/1880 KGNV: 77/1998

June 15: KJAX: 80/1880 KGNV: 78/1998

PRELIMINARY POINT TEMPS/POPS

JAX WATCHES / WARNINGS / ADVISORIES

FL...None. GA...None. MARINE...None.