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Area Forecast Discussion
Issued by NWS Jacksonville, FL
Issued by NWS Jacksonville, FL
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623 FXUS62 KJAX 201735 AFDJAX Area Forecast Discussion National Weather Service Jacksonville FL 135 PM EDT Sat Jul 20 2024 ...New AVIATION... .UPDATE... Issued at 1010 AM EDT Sat Jul 20 2024 For the latest NE FL and SE GA Daily Key Messages please visit: https://www.weather.gov/media/jax/briefings/nws-jax-briefing.pdf Sunny to partly sunny skies at this time with a few bands of cirrus clouds moving northeast over the area. Like yesterday, a moist-laden airmass continues with PWAT of 2.18 inches measured from JAX sounding. Should see plenty of cumulus forming in the late morning and aftn with numerous to widespread showers and storms forming by mid to late today. Current radar mosaic shows scattered convection across the central and western FL panhandle. The HRRR and the ARW Models are in good agreement showing showing first convective activity forming over the western zones along west coast sea breeze boundary and thermal troughing. Mean layer flow a bit faster than yesterday at about 15-18 knots through 500 mb. This may slightly support chances of some semi- organized clusters of storms, with strong gusty winds, frequent lightning, and locally heavy rainfall. Isolated severe storms are possible, with wind damage threat the main concern. The heavier rainfall areas will likely be along the east coast where max convergence is located due to the southwest prevailing flow meeting up with an east coast sea breeze that may make it inland by 4-6 pm to near the St Johns River in northeast FL and in southeast GA to near Jesup and Woodbine. The main forecast updates were to lower rain chances at least initially, but still forecasting upwards of 60-80 percent rain chances through the early evening hours. Max temps generally unchanged in the lower 90s with heat indices briefly around 108 but currently thinking too short duration for heat advisory at this time. Slightly adjustment for min temps tonight given the southwest, moist flow. For the marine forecast, only minor adjustments for the winds and seas, with observed seas at 41112 and 41117 currently 1 foot or so lower than forecast. Otherwise, main concern for boaters will be the strong wind gusts from storms this aftn and evening along with the lightning threat. && .NEAR TERM... (Today and Tonight) Issued at 322 AM EDT Sat Jul 20 2024 Southwest steering flow at the surface and in the mid levels combined with atmospheric PWATs around 2 inches will continue a near repeat of conditions from yesterday as late morning/early afternoon convection over inland areas that will track East to Northeast at 15-20 mph and reach the East Coast sea breeze that should reach into the US 17 and I-95 corridors in the mid/late afternoon hours and expect this convergence to trigger numerous to widespread showers and storms with strong/gusty winds to 50 mph along with heavy rainfall/localized flooding and frequent lightning, and similar to yesterday isolated severe storms with potential downburst winds to 60 mph are possible, mainly along the I-95 corridor of the Atlantic Coastal counties where storm mergers with the East Coast sea breeze are expected. This activity should then continue at strong to isolated severe levels as it pushes E-NE through the Atlantic Coastal Counties through the early evening hours and into the Atlantic Coastal waters around or just after sunset, with convection fading towards the late evening hours and ending by midnight. Timing of the onset of convection will determine eventual daytime Max temps, but overall expect widespread lower to middle 90s inland and around 90F at the Atlantic beaches and these combined with dewpoints into the middle 70s should push heat indices into the 104-108F range, likely just below or just briefly reaching Heat Advisory levels at this time. Overnight lows in the 70s over inland areas and near 80F at the Atlantic beaches. && .SHORT TERM... (Sunday through Monday night) Issued at 322 AM EDT Sat Jul 20 2024 A shift in the high pressure to the north-northeast of the region on Sunday will see the overall flow shift to be primarily from the south. This will allow the Gulf and Atlantic sea breezes to venture well inland. The daytime heating will see the development of showers and storms along the breezes, with activity picking up as the sea breezes merge during the afternoon between the I-75 and I-95 corridors. Most activity will dwindle during the overnight hours due to the loss of the daytime heating. By Monday, a southeasterly flow will become established as the high pressure shifts further north-northeast. This will setup the Atlantic sea breeze moving further inland towards the west. Near the I-75 corridor will be the likely area for the merger between the Gulf and Atlantic sea breezes during the afternoon hours on Monday, setting up the development of the stronger showers and storms of the day. Early afternoon showers will keep temperatures in check in the lower to mid 90s. Heat index values currently expected to stay just below criteria for heat advisory at this time for the weekend, but higher values will be expected along the coast. && .LONG TERM... (Tuesday through Friday) Issued at 322 AM EDT Sat Jul 20 2024 The high pressure to the northeast will continue the pattern of a far westward traveling Atlantic sea breeze. Showers and storms will develop along the Atlantic sea breeze as it moves to the west, but most convective activity likely to occur along the merger of the sea breezes over the western portion of the area. Activity will diminish each evening as the daytime heating is loss. Temperatures will trend near to above normal with highs in the low-mid 90s and lows in the 70s. && .AVIATION... (18Z TAFS) Issued at 125 PM EDT Sat Jul 20 2024 VFR clouds around at this time. A few showers and thunderstorms began to develop by about 16z-17z. Have continued to advertise TEMPO groups for TSRA this afternoon and into the evening, with just a slight adjustment to delay timing near CRG, JAX, and SSI. Showers and storms may contain brief wind gusts and low vsby to MVFR and IFR in heavy rainfall. The activity will concentration near or over the TAFs mainly in the 21z-01z time frame and then move offshore after about 02z. Mainly VFR overnight except for some MVFR vsby currently shown for VQQ. A repeat can be expected again Sunday for showers and storms, mainly aftn hours again. && .MARINE... Issued at 322 AM EDT Sat Jul 20 2024 No headlines expected over the next 5 days as high pressure ridge from the Western Atlantic will be across or just south of the local waters through early next week. This will continue a general south to southwest flow through the period at 10-15 knots with seas 2-4 ft, along with daily sea breeze along the local beaches from the Southeast. A few evening/nocturnal southerly wind surges could briefly reach into the 15-20 knot range, but not likely to last long enough to warrant any headlines. Main impacts will be offshore moving storms during the afternoon and evening hours with strong/gusty winds to 30-45 knots, heavy rainfall and dangerous lightning. Rip Currents: Marginal moderate risk of rip currents will continue through the weekend as mainly south to southwest flow becomes briefly onshore Southeasterly during the afternoon hours at the local beaches with surf/breakers of 2-3 ft. && .PRELIMINARY POINT TEMPS/POPS... AMG 73 92 73 93 / 60 80 40 60 SSI 76 89 77 91 / 70 60 40 50 JAX 74 93 75 94 / 60 70 30 60 SGJ 75 93 76 92 / 70 60 20 50 GNV 73 93 73 93 / 40 80 20 80 OCF 73 94 75 93 / 40 80 20 80 && .JAX WATCHES/WARNINGS/ADVISORIES... FL...None. GA...None. AM...None. && $$