


Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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324 FXUS62 KCHS 100557 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 157 AM EDT Thu Jul 10 2025 .SYNOPSIS... Weak high pressure will extend across the area into early next week. && .NEAR TERM /THROUGH TONIGHT/... Through This Evening: Another active day is expected across the Lowcountry and Southeast Georgia this afternoon and evening as the region becomes increasingly influenced by the cyclonic flow associated with the longwave trough that filling over eastern CONUS. Morning water vapor imagery showed what is left of the Tropical Upper Tropospheric Trough (TUTT) that was over the Bahamas Wednesday spinning just offshore the Georgia coast. This feature will weaken and translate farther offshore as the day progresses. A shortwave embedded within the weakening longwave trough will propagate across the Carolinas this afternoon/evening. Model cross section show a well-defined corridor of deep UVVs spreading east ahead of the shortwave which will interact with an increasingly moist and unstable atmosphere to support another round of numerous showers/tstms. Convection may be a bit delayed compared to Wednesday owing to slightly higher convective temperatures, but many areas are poised to see rainfall later this afternoon and evening as convection spreads east and eventually offshore. Given the favorable thermodynamic environment, 10/01z NBM pops were nudged up a bit with high end likely pops (around 70%) now advertised for all areas from mid/late afternoon through the mid-evening hours. Highs today will warm into the lower-mid 90s with dewpoints likely to mix out sufficiently to keep heat indices roughly in the 98-103 range with localized values reaching as high as 105 where dewpoints will pool near the sea breeze. Severe Weather: Modified soundings show moderate to locally strong instability developing this afternoon as temperatures warm into to the 90s. MLCAPE values as high as 3000-4000 J/kg are expected within a plume of PWATs well in excess of 2 inches. Shear (0-6km) is forecast to quite a bit stronger compared to the past few days, peaking around 20 kt during the afternoon and evening hours. While the shear is marginal for organized severe tstms, there will likely be several clusters of loosely organized convective clusters that occur where mesoscale processes dominate. Damaging winds from wet microbursts will likely be the primary convective hazard, although WBZ heights just above 11 kft and H-CAPE around 1200 J/kg could yield isolated instances of hail up to 1.25". In addition to the wind and hail threat, frequent cloud-to-ground/water lightning is likely to occur. The window for severe weather looks greatest from roughly 3PM-9PM. Heavy Rain/Flooding: The region remains situated within a plume of tropical moisture. PWATs are forecast to surge to 2.20-2.35" by late afternoon as moist, deep convection begins to trek east across the Lowcountry and Southeast Georgia. Forecast soundings show freezing levels will be lower than the past several days, likely in response to the passing shortwave aloft. Warm cloud processes may be somewhat limited because of this, but convection will likely remain efficient rain producers given the elevated PWAT values in place. Storm motions look much more progressive than 24 hours with the mean steering flow forecast to strengthen as the day progresses. Thankfully, this should limit the flood potential somewhat, but there could still be some localized rain amounts that exceed 4" based on the latest HREF neighborhood probabilities and ensemble localized probability matched mean (LPMM) output. There will likely be areas of minor flooding, mainly in low-lying and poor drainage areas. Flash flooding seems unlikely at this time. Overnight: Convection will gradually wind down through the night, although a risk for at least isolated showers/tstms will linger, especially at the coast. Lows will range from the lower 70s well inland to the upper 70s/near 80 at the beaches. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... The surface pattern will feature high pressure fixed offshore and a weak trough of low pressure across the Appalachians. A mid-level shortwave will push offshore the Carolina coast early Friday as ridging gradually builds over the Gulf and eventually centers over the Deep South by Sunday. There is no shortage of moisture (PWATs ~2.1") with west southwesterly flow continuously advecting Gulf moisture into the region. Some shear will accompany a moderately unstable airmass Friday (0-6 km bulk shear 15-20 kt and ~1500 J/kg MLCAPE) resulting in the possibility for an isolated strong to severe thunderstorm. Damaging winds would be the greatest concern with DCAPE values 800+ J/kg and favorable sounding profiles for wet microbursts. Storms could again produce bouts of heavy rain/downpours due to the high moisture content, but should have enough movement to limit flooding concerns. Beyond Friday, the area will start to see a slight downtrend in moisture advection Saturday night into Sunday as the "blocking" ridge becomes centered over the Deep South, noted by PWATs decreasing to 1.8 inches. However, enough moisture will be present for the development of isolated to scattered showers and thunderstorms both Saturday and Sunday, again mainly in the afternoons and evenings. A slight warming trend will continue through the short-term period, thanks to the building upper ridge. Friday`s forecast features max temps in the low to mid 90s, and about a degree or so warmer for Saturday. By Sunday, highs in the mid 90s will approach the upper 90s in some areas. Peak heat indices Sunday will range between 103- 106 degrees, just shy of our local Heat Advisory criteria of 108 degrees. We will continue to monitor in the event advisories are needed. Overnight lows both Friday and Saturday night will remain in the low/mid 70s away from the coast, and upper 70s at the beaches and Downtown Charleston. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... Ridging will continue to build over the Deep South early next week, meanwhile an upper level low could develop across the Caribbean and move toward the Southeast Coast by the middle of next week. Typical diurnal convection will continue Monday with scattered showers and thunderstorms forecast, and perhaps an increase in coverage possible as we near the middle of next week due to the potential disturbance aloft. Monday will follow with another day of high temperatures largely in the mid to upper 90s along with dew points in the mid 70s. Heat Advisories could be needed for some areas Monday. Above normal temperatures will continue into the middle of next week. && .AVIATION /04Z THURSDAY THROUGH MONDAY/... 10/06z TAF Discussion: KCHS/KJZI/KSAV: Tstms are poised to impact all three terminals again late this afternoon/evening as numerous showers and tstms impact the Lowcountry and Southeast Georgia. Window of impacts looks greatest between 21-00z at all sites and TEMPO groups highlighting TSRA were maintained. There are signals that a more concentrated area of convection could impact KSAV, so a more aggressive forecast to TSRA may be considered with the 12z TAF cycle, pending short term model trends. Extended Aviation Outlook: Periods of flight restrictions are likely at the terminals Friday afternoon/evening due to showers and thunderstorms impacting the area. Precip coverage should become more typical over the weekend, posing a more limited risk for flight restrictions. && .MARINE... Through Tonight: A south to southwest flow regime will prevail through tonight as high pressure holds well offshore. Winds will generally remain 15 kt or less, but could be as high as 15 kt with gusts to 20 kt near the land/sea interface and Charleston Harbor this afternoon as the sea breeze moves inland. Seas will average 2-3 ft. Clusters of strong to severe tstms may move offshore this evening and pose a risk for wind gusts in excess of 34 kt, frequent cloud-to-ground lightning and vsbys less than 1 NM in locally heavy rainfall. Special Marine Warnings may be needed. Friday through Tuesday: A fairly typical summertime pattern will remain in place with Atlantic high pressure centered offshore and a weak trough developing inland nearly each day. Relatively benign conditions are expected across the local waters as a result, with south to southwest winds 15 kt or less and seas between 2-4 ft, dropping to 1-3 ft late this weekend. Gusts up to 20 kt are possible along the coast and in the Charleston Harbor due to sea breeze influences each afternoon. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$