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

- Scattered Afternoon & Evening TStorms Expected on Sunday

- Hot & Humid Conditions through Monday. Heat Advisories Possible Sunday & Monday as Heat Indices Peak at 105 - 110 F

- Numerous Afternoon & Evening TStorms on Monday and Tuesday

- Low Potential for Slow Tropical Development off the Southeast U.S.

NEAR TERM /THROUGH TONIGHT/

Main Highlights Today and Tonight:

- Isolated strong storm potential along NE FL I-95 corridor and St Johns River Basin

- Hot and humid Today with heat indices 100-107 F

Prevailing flow will shift about to become more northerly over the course of the day as high pressure situated to the west drifts further towards the north and the influence of ridging from out of the east extending over the Florida peninsula begins to diminish. Isolated to widely scattered convection will develop through the afternoon stronger developments anticipated to occur along the diurnal sea breeze and areas of convergence, more likely along the I- 95 corridor and over areas south of I-10. High temperatures for this afternoon will rise into the lower to mid 90s over inland areas and in the lower 90s along the coastline. Overnight low temperatures will drop down into the lower to mid 70s over inland areas and in the mid to upper 70s for areas nearer to the coast. Heat index values are expected to be over 100 for portions of southeast Georgia and almost all of northeast Florida, however conditions for today are expected to remain below Heat Advisory levels.

SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/

Main Highlights This Period:

- Isolated to Widely Scattered Storms on Sunday Afternoon, Mainly South of Interstate 10

- Numerous Storms on Monday Afternoon and Evening, with Strong Storm Potential Along the U.S.-301 and I-95 Corridors

- Heat Advisory Conditions Possible for Portions of Our Area on Sunday and Monday Afternoons, with Heat Index Values Peaking in the 105-110 Range

"Heat Wave" ridging aloft building over the lower Mississippi Valley and the Ozarks on Sunday morning will extend its axis into the southeastern states on Sunday. Although model soundings indicate near climatological moisture values across our area, featuring PWATs of 1.8 - 2 inches, an increasingly subsident air mass, compliments of the expanding ridge to our northwest, will likely limit convective coverage across southeast GA and also along the Interstate 10 corridor. Isolated to widely scattered afternoon and early evening showers and thunderstorms are otherwise expected to develop for locations south of the I-10 corridor, mainly as mesoscale boundaries collide at inland locations. Less convective coverage and associated cloud cover will allow inland temperatures to soar to the mid and upper 90s on Sunday afternoon, with prevailing low level westerly flow delaying the development of the Atlantic sea breeze until the mid-afternoon hours, allowing coastal highs to climb to the mid 90s. Heat Advisory conditions may materialize on Sunday afternoon, especially at coastal locations, where heat indices may approach or exceed 108 degrees. Dewpoints at inland locations should fall to the upper 60s and lower 70s during the mid to late afternoon, which may keep heat index values just below the 108 degree threshold that would prompt at Heat Advisory.

"Heat Wave" ridging will shift slowly northward towards the Tennessee Valley from Saturday night through Sunday night, allowing a shortwave trough to progress down the southeastern seaboard. A Mesoscale Convective System (MCS) triggered by this shortwave trough may progress across the Carolinas, shifting offshore of the Outer Banks towards sunrise on Sunday. The tail end of this MCS may approach the Altamaha River towards or after midnight on Sunday night, possibly bringing some overnight activity to portions of inland southeast GA. Otherwise, any late afternoon convection that manages to develop on Sunday for locations south of I-10 should wind down shortly after sunset, with low level west-southwesterly flow keeping lows in the mid to upper 70s region-wide.

The aforementioned shortwave trough diving southward down the eastern periphery of "Heat Wave" ridging that will be in place over the Tennessee Valley will move across our region on Monday. This feature will push a surface trough across southeast GA during the afternoon and evening hours, with deep moisture pooling along and ahead of this trough and plenty of instability combining to ignite numerous thunderstorms across our area, mainly during the afternoon and evening hours. Strong storms will be possible, especially as mesoscale boundaries collide and storms pulse, with downburst winds of 40-55 mph, frequent lightning strikes, and heavy downpours expected within stronger activity.

Another oppressively hot and humid day is expected before storms erupt and expand in coverage later during the afternoon, with slightly stronger westerly flow likely providing highs in the mid to upper 90s all the way to coastal locations. Heat Advisory conditions may expand across most of our region, depending on timing of thunderstorm development, with heat indices generally in the 108-112 degree range across a good portion of our area. Thunderstorm activity will likely continue well into the evening and overnight hours as the surface trough shifts southward towards the I-10 corridor by sunrise on Tuesday, with lows remaining in the mid to upper 70s at most locations.

LONG TERM /TUESDAY THROUGH SATURDAY/

Main Highlights This Period:

- Monitoring the Gulf Stream Waters off the Southeastern Seaboard for Potential Tropical Development Towards Midweek

- Scattered to Numerous Showers and Thunderstorms Expected on Tuesday, Especially Across Northeast and North Central FL

- Daily Thunderstorm Coverage Shifts Southward, Especially by Thursday and Friday

"Heat Wave" ridging aloft will continue to build and shift slowly northward on Tuesday and Wednesday, with this feature becoming centered over the Ohio Valley by Tuesday. Meanwhile, weak surface troughing will continue to move slowly southward across our region, with high pressure building over the Mid-Atlantic states wedging down the southeastern seaboard in the wake of this southward moving trough. This evolution of the weather pattern will provide a deepening easterly flow regime across our area, which should provide some relief from the oppressive heat that is forecast on Sunday and Monday. Deep moisture will continue to pool along the surface trough axis across northeast and north central FL, developing numerous showers and thunderstorms during the early to mid afternoon hours, with activity shifting inland towards the I-75 corridor during the late afternoon and early evening hours. Convective coverage for locations north of I-10 is a little less certain on Tuesday, as slightly drier air may advect into southeast GA in the wake of the surface trough. Model blends depict inland highs reaching the lower 90s, with breezy onshore winds developing at coastal locations on Tuesday afternoon keeping highs in the upper 80s to around 90. Convection should begin to take on a more diurnal mode by Tuesday night and Wednesday as the surface trough begins to wash out and a drier air mass potentially advects into northeast FL. A light onshore breeze will likely keep lows closer to 80 at coastal locations, with inland lows generally in the low to mid 70s.

The aforementioned MCS (mentioned in the short term section) may shift over the warm Gulf Stream waters off the southeastern seaboard early during the upcoming week, with weak low pressure potentially developing beneath this convective cluster. This feature should be steered southward by the "Heat Wave" ridge to the northwest of our area, and the National Hurricane Center has assigned low probabilities for slow tropical development off the southeastern seaboard during the upcoming week. If this system materializes, it may eventually get steered westward in the general direction of the southeast GA or northeast FL coast later in the upcoming week. There remains quite a bit of uncertainty in the expected environment aloft and whether a favorable or unfavorable situation will be in place for this system to fester and develop over the warm Gulf Stream waters towards midweek.

Convective coverage should gradually wane later this week as the "Heat Wave" ridge begins to expand southward towards our area. Prevailing easterly flow on Wednesday and Thursday should keep temperatures close to seasonal averages, but above average temperatures appear likely towards Friday and the July 4th weekend.

AVIATION /00Z SUNDAY THROUGH 00Z MONDAY/

Last remaining storms will clear early during the early hours. VFR conditions are expected to develop overnight and through much of the TAF period. Mainly westerly winds after 12Z for TAF sites, with the Atlantic sea breeze moving inland around 17Z/18Z. Only include PROB30 group for GNV as convective activity currently looks to be limited over north central FL. Will re-evaluate in upcoming TAFs.

MARINE

Atlantic high pressure will extend westward across the Florida Peninsula just south of the area waters through the weekend. A pattern of overnight to early morning light westerly offshore winds and afternoon southeasterly winds expected due to sea breeze circulations. Afternoon and early evening isolated to scattered storms will develop across the nearshore waters each day into Sunday. A weak back door frontal boundary will approach the waters on Monday and stall over the waters Tuesday into Wednesday, supporting increased coverage for showers and thunderstorms for early next week.

Rip Currents:

A lower end moderate risk will develop during the late afternoon hours this weekend at area beaches as onshore winds become breezy following the passage of the sea breeze combined with a southeasterly ocean swell.

FIRE WEATHER

HIGH DAYTIME DISPERSION VALUES ACROSS INLAND PORTIONS OF - Southeast Georgia On Sunday

Scattered to numerous showers and thunderstorms will develop this afternoon through early this evening, with a few strong storms possible along the U.S. Highway 301 and 17 corridors in northeast and north central Florida. Only isolated to widely scattered afternoon and early evening thunderstorms are forecast on Sunday, mainly for locations south of the Interstate 10 corridor. Otherwise, prevailing westerly transport winds will combine with elevated mixing heights to yield good daytime dispersions this afternoon at moist inland locations, with fair values forecast for coastal locations as well as portions of north central Florida and the Suwannee Valley. Westerly transport winds will continue on Sunday, with breezy conditions developing across inland southeast GA that will create high daytime dispersion values, while lighter speeds across northeast and north central FL yielding generally fair values, while poor values prevail at coastal locations, where the Atlantic sea breeze will push inland early this afternoon and again early on Sunday afternoon. Transport winds will shift to west- northwesterly on Monday, with elevated mixing heights yielding generally good daytime dispersion values for inland locations. Numerous afternoon and evening showers and thunderstorms are forecast on Monday, with strong storms possible along the I-95 and U.S. Highway 301 corridors. FOG POTENTIAL AND OTHER REMARKS: Significant fog is not expected during the next several days. Stronger storms will be capable of producing strong and erratic wind gusts, along with frequent lightning strikes and heavy downpours, especially on Monday afternoon and evening.

HYDROLOGY

Minor flooding continues along lower portions of the Satilla River Basin, as water levels have recently fallen below flood stage at the gauge near Waycross. Minor flooding will continue near the gauge at Atkinson during the next several days, with a forecast crest late this weekend.

PRELIMINARY POINT TEMPS/POPS

AMG 75 96 76 96 / 10 10 10 50 SSI 79 95 80 95 / 0 10 10 60 JAX 77 98 78 98 / 10 10 20 70 SGJ 77 95 78 97 / 10 10 20 50 GNV 74 97 75 97 / 10 20 10 70 OCF 75 95 76 95 / 10 20 10 60

JAX WATCHES/WARNINGS/ADVISORIES

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