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

- Waves of Downpours and Embedded Thunderstorms Will Move Across Our Area through Late this Evening.

- A Few Strong Storms and Localized Flooding at Urban Locations Will be Possible Today and this Evening.

- Isolated to Widely Scattered Afternoon and Evening Thunderstorms Wednesday through Sunday.

- Summertime Heat and Humidity Returns Thursday through Monday, with Heat Advisory Conditions Possible this Weekend and Early Next Week.

NEAR TERM /THROUGH TONIGHT/

Main Highlights This afternoon and Tonight:

- Waves of Downpours and Embedded Thunderstorms Will Move Across Our Area through Late this Evening

- A Few Strong Storms and Localized Flooding at Urban Locations Will be Possible.

Early morning surface analysis depicts a wavy frontal boundary extending from near the Savannah River entrance westward across the Deep South, lower Mississippi Valley, and along the Red River Valley in northern Texas. Meanwhile, Atlantic high pressure (1024 millibars) centered to the east of the Bahamas continues to extend its axis westward across the FL peninsula and into the southeast Gulf. Otherwise, high pressure (1024 millibars) stretches from the Mid-Atlantic states across the Ohio and Tennessee Valleys and the southern Appalachians in the wake of the frontal boundary that was slowly pushing towards our region. Aloft...cutoff troughing over central and northern Alabama was located to the south of an expansive "heat wave" ridge that was blanketing the Upper Midwest, the Great Lakes, and the Plains states. Deep-layered Atlantic ridging remains suppressed to the south of our area, with fast low to mid level westerly flow in place between this ridge and the cutoff trough to the northwest of our region. This fast flow and embedded shortwave energy has touched off a small Mesoscale Convective System (MCS) that was moving quickly eastward across the FL Big Bend region, with mostly light showers or sprinkles migrating downstream from this feature across our area. Multi-layered cloudiness remains in place, with temperatures and dewpoints in the 70s region-wide at 08Z.

Cutoff troughing currently spinning over Alabama will become captured by the deep-layered "heat wave" ridge to its north, resulting in this feature retrograding westward across the lower Mississippi Valley this afternoon, reaching the Ozarks towards sunrise on Wednesday. Fast low and mid level westerly flow to the south of this cutoff trough will continue to propel shortwave energy across our region through around midnight tonight before drier air advects into our area during the predawn hours on Wednesday. Although the MCS feature currently migrating across the FL Big Bend and Apalachee Bay may weaken as it approaches the Suwannee Valley during the predawn hours, we expect waves of showers and thunderstorms to progress across our area today through late this evening, as a moist and unstable air mass remains in place. A low level jet of 25-35 knots at 850 millibars (around 5,000 feet) could cause convective cells to pulse and become strong at times through this evening, with stronger storms capable of producing downburst winds of 35-45 mph, along with frequent lightning strikes and torrential downpours. Convective coverage and intensity should then diminish after midnight tonight as troughing moves further away from our region, with ridging to our south building into our area and resulting in low level flow veering to northwesterly.

The frontal boundary currently positioned near the Savannah River entrance will sag southward towards the Altamaha River later today before this feature stalls overnight tonight and begins to weaken. We expect convergence to be maximized along and south of this boundary across southeast GA later this afternoon and throughout the evening, hopefully providing some beneficial downpours to interior southeast GA, which has mostly been devoid of significant rainfall thus far this month. Faster low level flow positioned across northeast and north central FL should result in waves of faster moving showers and thunderstorms throughout the day and evening hours, which should limit widespread heavy rainfall amounts. However, localized flooding cannot be ruled out if heavier cells train over urban or normally flood prone locations into the evening hours tonight.

Breaks in the multi-layered cloud cover in between rounds of convection should boost highs to the upper 80s and lower 90s this afternoon. Lows tonight will fall to the low and mid 70s area- wide.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/

Main Highlights During This Period:

- Reduced chances for storms.

Predominantly westerly flow will shift to become more out of the northwest by Thursday as high pressure in the vicinity of the Florida peninsula drifts further west towards Louisiana. Chances for daytime convection will be diminished on Thursday as drier air and more stable conditions move across over the forecast area. High temperatures through the latter part of the week will rise into the upper 80s and lower 90s for southeast Georgia and in the lower to mid 90s over northeast Florida with temps rising slightly into Thursday. Overnight low temperatures dropping down into the lower to mid 70s. Heat index values will are expected to range upwards of above 100, but is likely to remain below Heat Advisory criteria.

LONG TERM /FRIDAY THROUGH MONDAY/

Main Highlights During This Period:

- Daily bouts of showers and storms.

- Potential heat advisory conditions this weekend.

Typical seasonal pattern for this time of year with westerly and southwesterly flow, daily bouts of showers and storms, and hot weather will continue on through into Monday of next week. Above average temperatures, with max temps rising into the mid 90s, will continue through the end of the weekend and into next week with heat index values potentially rising to Heat Advisory levels through the period.

AVIATION /06Z TUESDAY THROUGH 06Z WEDNESDAY/

VFR conditions will prevail at the regional terminals through around 14Z. Occasional light showers will be possible overnight and early on Tuesday morning at the northeast FL terminals, with ceilings generally remaining above 5,000 feet. Ceilings may lower to around 1,500 feet after 14Z at the regional terminals as showers and thunderstorms potentially approach the GNV terminal from the west. TEMPO groups were included at the northeast FL terminals from 14Z- 20Z as convection pushes quickly eastward, with brief wind gusts up to around 30 knots and IFR visibilities during heavier downpours included. Convection should approach SSI after 19Z, but confidence was too low to include a TEMPO group at this time, as we opted for a PROB30 group through around 01Z Wednesday for brief wind gusts up to 30 knots and IFR visibilities during heavier downpours. A second round of convection could then impact the Duval County terminals and SGJ after 00Z WEdnesday, and we have inserted a PROB30 group for MVFR visibilities in heavy showers through around 06Z. Confidence was too low to include prevailing vicinity thunderstorms on Tuesday evening at this time. Southwesterly surface winds sustained around 5 knots overnight will shift to westerly towards 14Z, with speeds increasing to 5-10 knots outside of approaching convection. Westerly surface winds should then increase to 10-15 knots outside of potential convection after 16Z. Surface winds should then shift to west-northwesterly towards 00Z, with speeds diminishing to around 5 knots outside of potential convective impacts by 02Z Wednesday.

MARINE

A frontal boundary pushing slowly southward towards the Georgia waters will stall this afternoon, with this feature then weakening on Wednesday. Mainly light showers could impact the northeast Florida waters through the early morning hours on Tuesday, followed by additional rounds of showers and thunderstorms impact all of our local waters this afternoon and evening, with a few strong storms containing briefly gusty west winds and frequent lightning strikes possible. Scattered afternoon and evening showers and thunderstorms will be possible on Wednesday as prevailing winds briefing shift to northwesterly. Coverage of showers and thunderstorms will then decrease by Thursday as the frontal boundary dissipates, with only isolated to widely scattered late afternoon and early evening activity possible for the near shore waters through Friday as a prevailing westerly flow continues during the overnight and morning hours each day. Surface troughing developing over the southeastern states this weekend could bring scattered afternoon and evening showers and thunderstorms to our local waters as offshore winds prevail.

Rip Currents:

Prevailing offshore winds and low surf heights will keep the rip current risk low at area beaches throughout this week.

FIRE WEATHER

- Areas Of High Dispersions Through Thursday.

The region will be between high pressure to the south and a gradually weakening frontal zone to the north this week. While daily thunderstorm chances are forecast, above average chances can be expected before midweek. Temperatures will be above average, with a trend upward later in the week.

Fog Potential and other remarks: Significant fog potential is not expected Tonight. Erratic wind gusts possible in and near thunderstorms, and at times, at a distance due to outflows.

PRELIMINARY POINT TEMPS/POPS

AMG 89 72 90 73 / 70 40 30 10 SSI 91 74 92 77 / 70 60 40 20 JAX 91 73 93 74 / 60 40 40 10 SGJ 92 75 93 76 / 60 20 50 10 GNV 91 73 93 74 / 40 20 40 10 OCF 91 73 93 75 / 40 10 30 0

JAX WATCHES/WARNINGS/ADVISORIES

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