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

- Severe Thunderstorm & Flood Risk this Afternoon & Tonight. Mainly Along and North of the I-10 Corridor. Hazards: Damaging Wind 40-60 mph, Localized Flash Flooding, and Frequent Lightning

- Moderate Rip Current Risk Northeast Florida Beaches Today

- Heat Index near 107 This Afternoon

- Daily Afternoon & Evening Thunderstorms This Coming Week

NEAR TERM /THROUGH TONIGHT/

Highlights Through Tonight:

- Severe Thunderstorm and Flooding Risk this Afternoon & Evening

Ahead of an incoming cold front that will bring potential for severe weather later this afternoon through the late evening, we will see scattered to numerous diurnally driven showers and storms across the area. With westerly winds, the two sea breezes will collide closer to the east coast, enhancing convective coverage near I-95 this afternoon. Plenty of instability and moisture present will pose a threat for strong to isolated severe thunderstorms, mainly from boundary collisions, causing gusty winds. In addition, we will see a localized flooding threat primarily for the northeast Florida and southeast Georgia coasts, but also later on tonight for inland southeast Georgia. Urban and other typical flood prone areas will be more at risk for flooding today.

Outside of the east coast afternoon/evening summertime storms, a front will sink southward this evening, prompting additional thunderstorm activity, over southeast Georgia. This area is under a Marginal to Slight risk of severe storms, with damaging winds as the primary hazard. Overall, storms will begin to fizzle out around midnight, with some lingering showers and isolated storms possible through the night as the front stalls near the Florida/Georgia border.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/

Main Highlights This Period:

- Localized Flooding Rain Threat

- Daily Thunderstorms Chances

The weak cold front will be over central or northern parts of the forecast area Monday morning, but is expected to gradually shift southward to north central FL by Tuesday. On Monday, should see weak north-northeast sfc flow over inland southeast GA, but southwest or variable/east sfc flow for northeast FL. Aloft, the tail end of a mid level trough will push through the area Monday, followed by northeast mid level flow on Tuesday as a high pressure center in the mid levels moves into the TN valley area. No shortage of moisture with PWAT of about 2.2 inches is noted for Monday, and due to the proximity of the front, will lead to high shower/storm coverage, at least numerous. However, more scattered activity expected northwest of Alma GA. MLCAPE ranging from 2000-2500 J/kg over the region and sea breezes/outflow boundaries will be present. This should promote locally heavy rainfall and some local flooding threat mainly the srn 2/3rds of the area. Some convective activity will linger during the overnight hours Monday night, with the best chances probably over the marine waters and the immediate coast. As the west-east oriented front and associated troughiness begin to slip southward Tuesday, low level flow becomes increasingly northeast and east. Convergent onshore flow coupled with high airmass moisture content (PWATs 2.1 inches) will result in coastal convection that shifts gradually inland during the midday and afternoon hours. Still a localized flooding rainfall threat, but perhaps not quite as high as Monday's forecast. Coverage will at least be numerous during the day, with some isolated shower activity overnight into early Wednesday morning near the coastal areas.

Currently, total rainfall amounts we are forecasting ranges from 0.50 to about 1.25 inches, but can see potential for localized 4+ inches.

With the cold front making its way across the area, slightly cooler temperatures will develop from north to south. On Monday, SE GA locations will likely top out in the upper 80s, while NE FL will be in the upper 80s to lower 90s. By Tuesday, highs in the mid to upper 80s will develop behind the front.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Main Highlights This Period:

- Daily Thunderstorms Chances

The weak frontal boundary mentioned in the short term period may be stalled over north central FL early Wednesday and then becomes more diffuse and ill-efined by Thursday as low level shifts from easterly to southeasterly to south to southwest on Thursday. This is due to the mean layer high over the NC outer banks moving eastward into the Atlantic and mid to upper level trough moving into the eastern U.S. Guidance suggests another cold front will push towards the area by the upcoming weekend by not moving into the southeast GA zones by Saturday. Thus will continue to see deep and moist southwest flow Thursday through Saturday continuing a chance of showers and storms each day.

Fairly high coverage of showers and storms (up to 60-70 percent coverage) on Wednesday, especially inland areas, looks to fall slightly to the scattered to numerous range (or about 45-65 percent) Thursday through Saturday.

Temperatures will generally be in the upper 80s to lower 90s through the period.

AVIATION /18Z SUNDAY THROUGH 18Z MONDAY/

Outside of convection and showers, VFR conditions are forecast today. Showers and storms will pick up for the area this afternoon and evening, with impacts likely from around 20-01Z. Another round of storms will enter southeast Georgia associated with a front, with impacts to SSI lasting through around 02-03Z. Vicinity showers/light rain will be possible for most of the sites through at least 06Z, with potential for MVFR ceilings/mist closer to sunrise. Winds will be variable overnight as the front moves south towards the state border.

MARINE

High pressure will continue south of the local waters today as a front approaches from the northeast. Strong thunderstorms are possible this afternoon and evening as the front approaches. The front will stall across north Florida Monday, then shifts south of the waters Monday night into Tuesday as high pressure strengthens to the northeast. A brief period of Small Craft Exercise Caution conditions is possible mainly over the Georgia waters Tuesday as a coastal trough develops offshore. The coastal trough weakens Wednesday into Thursday. Friday into Saturday, high pressure extends across south Florida with a return of westerly winds and the afternoon east coast sea breeze nearshore.

Rip Currents: Rip current risk increases from north to south Monday as onshore flow develops with moderate risk likely for all local beaches. By Tuesday, solid moderate to possibly high rip current due to stronger and more persistent ENE onshore winds.

FIRE WEATHER

- Patchy Low Dispersions Northeast Florida On Monday

West to southwest winds continue rest of today except for an east coast sea breeze for eastern zones. Expect isolated showers and thunderstorms at 2 PM to expand in coverage to numerous by late in the afternoon through the late evening hours. A risk for stronger to severe storms is forecast from about 3 PM to 11 PM across southeast Georgia to near Interstate 10 as a weak front approaches. In addition, a slight risk of excessive rainfall is forecast mainly for southeast GA late this afternoon through late evening.

The front is expected to shift southward across northeast Florida Monday through Monday night. Low daytime dispersion expected Monday and possibly Tuesday due to more cloudiness and elevated rain chances. Surface winds and transport winds will transition to northeast to east behind of the front on Tuesday with elevated rain chances expected again.

Fog Potential: Gusty and erratic winds will occur with thunderstorm activity. Patchy inland morning fog possible each day.

HYDROLOGY

Coastal water levels begin to increase next week with the approach of the New Moon on Sept 11th and breezy onshore easterly winds late Monday through Wednesday, with the peak winds across the local waters and coast Tuesday. At this time, extended probabilistic guidance keeps water levels below action stage late Tuesday through Wednesday both along the local Atlantic coast and within the St. Johns River basin.

PRELIMINARY POINT TEMPS/POPS

AMG 73 87 72 86 / 60 80 30 60 SSI 76 86 76 86 / 40 80 80 80 JAX 74 88 73 87 / 60 90 50 80 SGJ 75 87 74 86 / 40 80 60 70 GNV 74 89 72 88 / 40 90 40 80 OCF 74 89 73 89 / 30 80 30 80

JAX WATCHES/WARNINGS/ADVISORIES

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