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Area Forecast Discussion
416 FXUS62 KCHS 260151 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 951 PM EDT THU AUG 25 2016 .SYNOPSIS... High pressure will prevail into the weekend. A weak surface trough will develop over the region by late weekend and will persist through the middle of next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Thursday was the 65th straight day of 90 degrees or greater at Savannah (KSAV). Tonight: The bulk of the atmosphere is under the influence of strong anticyclonic flow, with the exception of the upper levels where analysis reveals a weak TUTT low spiraling over NE Florida and drifting SW. Considerable dry air (PWat 1.15 inches at 00Z as per KCHS sounding) within the large scale sinking motion and the lack of any appreciable low level convergence will allow for another rainfree night. If there are any showers they will stay out near the western wall of the Gulf Stream closer to daybreak. Mainly clear to clear skies and calm or light winds away from the immediate shoreline will allow for good to excellent radiational cooling. But since dew points are not as low as 24 hours ago, we won`t get quite as cool as last night. Expect minimum temps near or just below normal for this time of year. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... Friday: A large mid/upper lvl ridge of high pressure will prevail over the Southeast late week, generally favoring rain-free conditions over all locations while subsidence occurs and pwats remain at or below 1.0 inch for most of the area. In general, high temps should peak in the low/mid 90s. Overnight lows will range in the lower 70s inland to mid/upper 70s near the coast Friday night. Saturday and Sunday: Very little change is anticipated in the overall pattern this weekend into early next week. However, models continue to suggest that the mid/upper ridge of high pressure responsible for dry weather over the Southeast will nudge further north/northeast as a trough of low pressure begins to develop over the region late Sunday. The setup should allow a more direct onshore flow and increasing levels of moisture to advect over the region from the Atlantic. Given sufficient sfc heating each day, expect at least slight chances of showers/thunderstorms during peak diurnal heating each day. However, the best chance of precip will likely remain in southern Georgia counties on Saturday, before increasing coverage in Southeast Georgia and Southeast South Carolina on Sunday, mainly due to a more active seabreeze. Overall, high temps are expected to range in the low to mid 90s away from the coast each day. Overnight lows will range in the low/mid 70s away from the immediate coast. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Independent of the development of a tropical entity that evolves from a disturbance located near Hispaniola and moving WNW toward the Florida peninsula, a shift to deep-layered troughing should translate to a greater chance for showers/thunderstorms during this period, especially during the Tuesday through Thursday time frame. After another day with high temps in the lower/mid 90s Monday, the greater potential for clouds/precipitation is reflected in near normal temperatures in the upper 80s/lower 90s Wednesday and Thursday. Lows should range in the mid 70s inland to around 80 along the coast through this period. As of Thursday evening, the National Hurricane Center indicated a medium chance for tropical development within a zone from north of Hispaniola to southern Florida within 5 days, and guidance generally agrees that a tropical system will be located in the vicinity of south Florida later this weekend. Thereafter, guidance has generally trended toward a solution which turns the tropical system toward the north, either over the Gulf of Mexico or near the western Florida coast, perhaps carrying low pressure over land and across our area with a threat of heavy rain and potentially severe weather for mid to late week. However, due in part to the uncertain rate of weakening of the deep-layered ridge currently over the area and a highly uncertain tropical cyclone track/intensity forecast beyond this weekend, the latest forecast does not explicitly account for any impacts from a recurving tropical cyclone next week. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... VFR. Extended Aviation Outlook: VFR conditions are expected at both CHS and SAV terminals. && .MARINE... Tonight: A narrow ridge of Atlantic high pressure squeezed between a cold front to the distant NW and lower pressures to the SE will prevail across the local waters. E winds around 12-18 kt early on will diminish to 15 kt or less thereafter. Winds will back to more solid NE or even NNE flow late near the coast and in Charleston Harbor due to the cooling land breeze. A little 1-2 ft swell from the remnants of "Fiona" and persistent onshore fetch will combine with shorter period wind waves to give us average seas of 3-4 ft. Friday through Tuesday: High pressure will dominate the coastal waters through Saturday, before giving way to a weak trough of low pressure advancing into the area this weekend. The setup will favor east/northeast winds between 10-15 kts with gusts as high as 20 kts in offshore Georgia waters into early next week, before winds become more east/southeast in response to low pressure entering the area. Seas will slowly build from 2-4 ft to 3-5 ft this weekend into early next week. There is a chance that offshore Hurricane Gaston could push a long period swell as high as 6 feet into waters beyond 20 nm early next week. Rip currents: Persistent onshore winds and a small long period swell could begin to produce an elevated risk of rip currents this weekend. A larger and longer period swell produced by Hurricane Gaston could begin to reach the coast early next week and this could set the stage for stronger/more frequent rip currents. && .TIDES/COASTAL FLOODING... Tides have been running above extratropical surge guidance but have remained just below Coastal Flood Advisory levels for the past couple of days. This scenario will likely repeat around the times of the afternoon high tides through this weekend as E/NE winds prevail. There is a chance that the influence of the Sept. 1 new moon and a larger swell produced by offshore Hurricane Gaston could combine to push evening high tides past Coastal Flood Advisory levels next week. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM... SHORT TERM... LONG TERM...SPR AVIATION... MARINE... TIDES/COASTAL FLOODING...