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

- Strong to Isolated Severe Thunderstorms and Localized Flooding Possible Across Southeast GA Late this Afternoon and Evening.

- Strong Thunderstorm Potential Along the Northeast FL Coast During the Early to Mid-Afternoon Hours Today.

- Additional Rounds of Showers and Thunderstorms Possible Overnight Tonight, with Widespread Activity Continuing on Tuesday.

- Heat and Humidity Returns Late this Week and into the Upcoming Weekend as Thunderstorm Coverage Decreases.

NEAR TERM /THROUGH TONIGHT/

Main Highlights This afternoon and Tonight:

- Strong to Isolated Severe Thunderstorms and Localized Flooding Possible Across Inland Southeast GA Late this Afternoon and Evening.

- Strong Thunderstorm Potential At Coastal Locations this Afternoon.

- Additional Rounds of Showers and Thunderstorms Possible Overnight Tonight, Especially Along the I-10 Corridor.

Early morning surface analysis depicts a wavy frontal boundary stretching from coastal south Carolina westward across the southern Appalachians and the Tennessee Valley through the Ozarks and southern Plains states. Meanwhile, Atlantic high pressure (1021 millibars) positioned east of the Bahamas continues to extend its axis westward across south FL and the southeastern Gulf. Otherwise, strengthening high pressure (1024 millibars) was expanding from the Upper Midwest eastward across the Ohio Valley and the Mid-Atlantic states in the wake of the frontal boundary that was pushing slowly southward towards our area. Aloft...a potent shortwave trough over the southern Appalachians was in the process of cutting off from the main flow pattern as it meanders southward, with this feature suppressing deep-layered ridging south of our area. A "heat wave" ridge expanding from the eastern Rockies and the northern Plains states towards the Upper Midwest and the Great Lakes states was otherwise creating a highly amplified "blocking" pattern over the eastern half of the nation. Latest GOES-East derived Total Precipitable Water imagery indicates that deep tropical moisture has overspread our region, with PWATs ranging from 1.9 - 2.2 inches. Mid and high altitude cloud cover was slowly thinning out across our area as of 08Z, with temperatures and dewpoints in the 70s area-wide.

The potent shortwave trough over the southern Appalachians will cutoff today as it sinks southward across the Tennessee Valley, with this feature then becoming steered southwestward towards the lower Mississippi Valley tonight as it becomes captured by the expanding "heat wave" ridge over the Upper Midwest and the Great Lakes states. Troughing aloft will continue to support a slow moving, wavy frontal boundary that will slide towards the Deep South and the lower Mississippi Valley today and tonight. Deepening westerly flow to the south of this trough and its associated frontal boundary is expected today, which will continue to advect tropical moisture across our area.

The main forecast question will be cloud cover this morning, which will determine how unstable our atmosphere will become today, particularly over northeast and north central FL. There is not much in the way of shower activity upstream of our area over Apalachee Bay and the northeast Gulf, and recent satellite trends depict a slow thinning of mid and high altitude cloudiness. Convection may not begin over areas upstream from our region until the mid-morning hours, allowing for enough heating an instability to create numerous showers and thunderstorms along the inland moving Gulf sea breeze boundary by the late morning and early afternoon hours. Activity should race towards the Atlantic coast during the mid-afternoon hours, where convection may interact with a pinned Atlantic sea breeze boundary east of the I-95 corridor that could cause a few storms to "pulse" and become strong across coastal northeast FL before moving offshore late this afternoon. Stronger activity could produce brief wind gusts of 35-45 mph, frequent lightning strikes, and briefly heavy downpours. Highs today will be held to the 85-90 degree range across inland northeast and north central FL, ranging to the lower 90s at coastal locations, where convection may not arrive until the mid-afternoon. Heat index values will generally rise to the 100-105 degree range along and east of the U.S. Highway 301 corridor.

Convective outflows moving northward will ignite numerous showers and thunderstorms during the mid to late afternoon hours across southeast GA, where activity could be enhanced by a developing 35-45 knot west-southwesterly low level jet positioned at 850 millibars (around 5,000 feet). Strong to isolated severe thunderstorms will be possible across southeast GA later this afternoon, with heavy downpours potentially focusing over inland southeast GA, where deeper tropical moisture will be pooling ahead of the approaching frontal boundary. The Weather Prediction Center has indicated a "Slight" risk (level 2 of 4) for excessive rainfall this afternoon from areas around Waycross and points northward in interior southeast GA this afternoon, while a "Marginal" risk (level 1 of 4) is in place elsewhere across our area. Localized flooding will be possible today, mainly at more urban and normally flood prone locations across southeast GA, where convection could linger slightly past sunset this evening. Stronger storms pulsing over southeast GA could produce downburst winds of 40-60 mph, along with frequent lightning strikes and torrential downpours. Highs will generally climb to the upper 80s and lower 90s, with heat index values peaking in the 100-105 degree range for locations east of U.S.-301.

Strong storms and torrential downpours may linger into the early evening hours across interior southeast GA before activity lifts north of the Altamaha / Ocmulgee River basins by midnight. Meanwhile, the aforementioned strong low level westerly jet could propel another round of convection across Apalachee Bay early this evening, with a second episode of showers and thunderstorms potentially impacting the Suwannee Valley and the I-10 corridor late this evening. Cyclonic flow around the trough digging towards the Deep South and the lower Mississippi Valley may also ignite convection along the FL Nature coast towards sunrise on Tuesday. Cloud cover and low level westerly flow will generally keep low temperatures in the low and mid 70s area- wide tonight.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/

Main Highlights During This Period:

-Increased storm potential on Tuesday with greatest chance for strong to severe thunderstorms and heavy rainfall north of I-10.

Predominantly westerly flow through Tuesday and then shifting to become more out of the northwest on Wednesday as high pressure over the Florida peninsula moves eastward and drifts northward towards the Gulf. Pattern of daily showers and storms will continue through midweek with convection expected to be more widespread on Tuesday with more dense developments expected to occur over southeast Georgia, nearer to the frontal boundary to the north. High temperatures through midweek will rise into the upper 80s and lower 90s for southeast Georgia and in the lower to mid 90s over northeast Florida with temps beginning to increase on Wednesday. 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 /THURSDAY THROUGH SUNDAY/

Main Highlights During This Period:

- Reduced Chances for Afternoon and Evening Thunderstorms.

- Heat and Humidity Returns Late this Week and into the Upcoming Weekend.

Easterly prevailing flow will continue through the week as high pressure situated to the south continues to extend to to the west and north with flow becoming less uniform by the weekend as high pressure over waters to the east strengthens off the coast. Daily bouts of showers and storms will continue through into the weekend with convection expected to be less widespread than earlier in the weak as the front to the north become less defined. Above average temperatures, with max temps rising into the mid 90s, will continue through the end of the week and into the weekend with heat index values potentially rising to Heat Advisory levels through the period.

AVIATION /06Z MONDAY THROUGH 06Z TUESDAY/

Periods of MVFR to IFR conditions are expected overnight at VQQ. Otherwise, VFR conditions will prevail at the regional terminals through at least 15Z. Showers and thunderstorms developing on Monday morning along the FL Big Bend and Nature Coasts will push quickly eastward, with convection expected to approach GNV after 15Z. TEMPO groups were introduced during this TAF cycle due to increasing confidence in timing between 16Z-19Z at GNV, where brief wind gusts up up 30 knots and IFR visibilities during heavier downpours are forecast. The TEMPO period for these impacts should be narrowed down further during the 12Z TAF cycle. Convection should then approach VQQ after 16Z and then JAX and CRG after 17Z, with activity then reaching the SSI and SGJ coastal terminals towards or just after 18Z. TEMPO groups were also introduced at the Duval County terminals and the coastal terminals for brief wind gusts up to 30 knots and IFR visibilities during heavier downpours, with activity expected to push offshore before 23Z. Showers could linger into the early evening hours at SSI, but VFR conditions will generally prevail after 00Z Tuesday, with visibility restrictions possible at VQQ towards the end of this TAF cycle on Monday night. West- southwesterly surface winds will remain sustained around or less than 5 knots overnight at the regional terminals. Westerly surface winds are expected to develop towards 14Z, with speeds increasing to around 10 knots by 16Z. A pinned Atlantic sea breeze boundary may shift surface winds to southerly around 18Z before convection arrives at the coastal terminals.

MARINE

A frontal boundary pushing slowly southward down the South Carolina coast will approach the Georgia waters by Monday evening, with this feature then stalling over the Georgia waters on Tuesday before weakening on Wednesday. Showers and thunderstorms will impact our local waters earlier during the afternoon hours through Wednesday, with a few strong storms containing briefly gusty westerly winds and frequent lightning strikes possible. Coverage of showers and thunderstorms will then decrease by Thursday and especially on Friday and Saturday as the frontal boundary dissipates, with only isolated to widely scattered late afternoon and early evening activity possible for the near shore waters as a prevailing westerly flow continues during the overnight and morning hours each day.

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 Tuesday 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 early in the week. 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 90 73 88 72 / 80 60 70 40 SSI 90 76 90 76 / 70 50 80 50 JAX 90 74 91 73 / 70 30 70 40 SGJ 91 75 92 75 / 70 20 70 30 GNV 88 73 91 73 / 70 30 60 10 OCF 89 74 92 75 / 60 20 40 10

JAX WATCHES/WARNINGS/ADVISORIES

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