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Area Forecast Discussion
543 FXUS62 KCHS 240739 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 339 AM EDT WED AUG 24 2016 .SYNOPSIS... High pressure will prevail into this weekend. A surface trough will push into the region by late this weekend and will persist through the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... An expansive upper ridge will persist while slightly drier/cooler surface high pressure off the Northeast coast will continue to extend southwest into the area. Other than a few stray showers or tstms over the outer GA coastal waters, dry weather anticipated through tonight. Highs will top out in the lower 90s inland while a robust afternoon sea breeze limits temps to no higher than the upper 80s closer to the coast. Mostly clear skies, mid/upper 60s dewpoints and diminishing winds tonight will produce rather unseasonable low temps in the upper 60s inland, with lower 70s coastal. && .SHORT TERM /THURSDAY THROUGH SATURDAY/... Thursday through Friday: Deep layered high pressure will remain in place over the region. Isolated showers could push onshore into SE GA coastal counties south of Tybee Island, especially Thursday afternoon. Otherwise, subsidence will produce a dry/capped environment, and most areas will remain rain-free. High temps in the upper 80s/lower 90s Thursday will warm into the lower/mid 90s away from the coast Friday. Maximum heat index values should remain below 100F across the region Thursday, and heat index values around 100F should remain confined to far southern/inland counties Friday. Expect low temps in the lower/mid 70s inland and 75-80F on the beaches both nights. Saturday: The center of the sprawling eastern CONUS ridge will shift slightly east, and the surface high will weaken to some degree. This could open the door for an increasingly moist onshore flow, especially across southern counties/along and south of I-16 where slight chance pops have been introduced into forecasts. Otherwise, high temps will range from the upper 80s near the coast to the lower/mid 90s inland. Increasing dewpoints will translate to expanding coverage of heat index values around 100F. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... The eastern CONUS upper ridge and associated surface high are expected to weaken this period. Details regarding this process differ, but a reasonable scenario includes general weakening of subsidence/capping aloft and a trend toward surface troughing. This should, in turn, support an increasing chance of showers/thunderstorms as onshore flow/moisture transport persist. Latest forecasts include a transition from slight chance POPs north/chance POPS south Sunday-Monday to greater coverage of chance POPS Tuesday-Wednesday, especially during the daytime hours. Meanwhile, odds favor slightly above normal temperatures through much of the period. Guidance generally agrees that a tropical cyclone could be approaching south FL by later this weekend. However, solutions diverge greatly thereafter, so this feature does not directly factor into our forecasts through the middle of next week. && .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/... VFR will prevail through 06Z Thu. Extended Aviation Outlook: VFR. && .MARINE... High pressure will continue to build over the waters from the northeast, maintaining a modest northeast flow through tonight. Conditions expected to remain below Small Craft Advisory levels though coastal areas may see some 20 kt gusts with a robust afternoon sea breeze. Thursday through Monday: High pressure will dominate the coastal waters Thursday through Saturday, then the high will weaken and will give way to a trough of low pressure which will advance into or develop over the waters this weekend. With occasional/minor variations, east/northeast winds should average 10-15 kt with gusts 15 to 20 kt through this period. Through late week, combined seas will average 2-4 feet, although seas as high as 5 feet will occasionally push into the outer GA waters. Then, the long fetch/duration onshore flow and the possible arrival of larger, long period swell emanating from TC Gaston will increase the chance for Small Craft Advisory conditions beyond 20 nm this weekend into early next week. Rip currents: Onshore winds and a small long period swell will persist this week, perhaps elevating the risk of rip currents by late week. There is a chance that a larger, long period swell created by TC Gaston swell could reach the beaches as early as this weekend. If this occurs, the chance for rip currents will increase significantly this weekend into next week. && .TIDES/COASTAL FLOODING... A long duration of E/NE winds will support elevated high tides through at least this weekend. Extratropical surge guidance has consistently held tides at least one-half foot below Coastal Flood Advisory levels through the period. However, there remains a low probability that afternoon high tide levels could slightly exceed forecasts and approach Coastal Flood Advisory thresholds especially along the SC coast. && .EQUIPMENT... The Metter NOAA Weather Radio All Hazards station, WWH-25 will be off the air until further notice. The telephone company is investigating the problem. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...JRL SHORT TERM...SPR LONG TERM...SPR AVIATION...JRL/SPR MARINE...JRL/SPR TIDES/COASTAL FLOODING... EQUIPMENT...