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Area Forecast Discussion
138 FXUS62 KCHS 242019 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 419 PM EDT WED AUG 24 2016 .SYNOPSIS... High pressure will prevail into the weekend. A weak surface trough will push into the region by late weekend, then persist through the middle of next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... An expansive upper ridge will persist while slightly drier/cooler surface high pressure off the Northeast coast will continue to extend southwest into our area. Other than a few stray showers over the coastal waters, dry weather is anticipated. Mostly clear skies, mid/upper 60s dewpoints and diminishing winds will allow low temperatures to fall into the upper 60s inland, with lower 70s coastal. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/... Thursday and Friday: A large mid/upper lvl ridge of high pressure will prevail over the Southeast late week, generally favoring a dry forecast over most locations. However, we can not rule out a few showers and/or isolated thunderstorm drifting onshore in Southeast Georgia or well inland where a weak sfc trough approaches the region from the northwest late week. At this time, the front should have minimal impact to the forecast area while temps continue to modify a few degrees under the persistent ridge aloft. In general, high temps should peak in the upper 80s to lower 90s on Thursday, followed by low/mid 90s on Friday. Overnight lows will also show a warming trend, ranging in the upper 60s to lower 70s Thursday night, then lower 70s inland to mid/upper 70s near the coast Friday night. Saturday: Very little change is anticipated in the overall pattern this weekend. However, models generally agree that the mid/upper ridge of high pressure over the Southeast will nudge further north/northeast, allowing an east/northeast flow to become more directly onshore. The setup will favor some moisture advection from the Atlantic while afternoon temps peak in the low/mid 90s. Given the moisture and heating, slight chances of showers/thunderstorms will remain in the forecast with greatest chances occurring in Southeast Georgia where a seabreeze should be slightly more active. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... 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 /19Z WEDNESDAY THROUGH MONDAY/... VFR will prevail through 18Z Thu. Extended Aviation Outlook: VFR conditions are expected at both CHS and SAV terminals. && .MARINE... High pressure to the north will maintain northeast winds tonight. Expect sustained winds around 15 kt with some gusts up to 20 kt this evening. Winds will ease to 5-10 kt after midnight, as the gradient weakens slightly. Seas will be 2-3 ft within 20nm and 4 ft for AMZ374. Thursday through Monday: High pressure will dominate the coastal waters through Saturday, before giving way to a weak trough of low pressure which will advance into or develop over the waters this weekend. With occasional/minor variations, east/northeast winds should average between 10-15 kt with gusts as high as 20 kt through this period. Through late week, seas will range between 2-4 feet, although seas as high as 5 feet will occasionally push into the outer Georgia 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. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM... SHORT TERM... LONG TERM...SPR AVIATION... MARINE... TIDES/COASTAL FLOODING... EQUIPMENT...