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Area Forecast Discussion
199 FXUS62 KCHS 290805 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 405 AM EDT MON AUG 29 2016 .SYNOPSIS... Tropical Depression Nine is expected to intensify into a tropical storm and track from the eastern Gulf of Mexico northeast across northern Florida and off the Southeast U.S. coast late in the week. Cooler and drier high pressure will then return from the north this weekend. && .NEAR TERM /THROUGH TONIGHT/... Deep layered E to NE flow will persist today due to a closed upper low drifting west and an associated surface trough lingering over our coastal waters. As of Sunday evening`s sounding, the Precipitable Water value shot up above 2 inches after several days closer to 1.3 inches. Through daybreak only isolated showers will continue over the coastal waters with a few moving onto the beaches before dissipating. After sunrise we should see increasing coverage of showers, with some tstms possible in the afternoon. Given the continued upper height falls, deep moisture, increasing low-level instability and a decent afternoon sea breeze, we are carrying 30-40% rain chances in most locations. High temps will reach the low to mid 90s inland while coastal locations top out in the upper 80s. Tonight, most showers or tstms over land areas will diminish after the sun sets. Then, showers will become more numerous over the coastal waters, especially the GA waters as the coastal trough strengthens under the lingering upper low. Some showers may move onshore especially late tonight but the brunt of the convection will remain over the ocean. && .SHORT TERM /TUESDAY THROUGH THURSDAY/... Weak low pressure system could develop off the Southeast U.S. coast Tuesday night before tracking northeast into Thursday. However, the main concern as we head toward the end of the period will be Tropical Depression Nine which is forecast by the NHC to intensify into a tropical storm in the eastern Gulf of Mexico Tuesday and then track northeast across northern Florida. Still some uncertainty regarding this system but confidence is pretty high that there will be minimal impacts through this period. Otherwise, general troughing will persist with the deepest tropical moisture likely to remain south and east of the area. Thus, rain chances should not be much more than typical for this time of year, which is about 30 percent. Also, rain amounts will generally be limited to about an inch or less most places through the period. Temperatures are likely to be slightly above normal, mostly lower 90s for highs and mid 70s for lows. && .LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/... The latest forecast from the NHC indicates a tropical storm will be moving off the northeast FL coast Thursday night and then staying offshore as it moves away from the GA/SC coasts through late week. This will be followed by high pressure building from the north this weekend into early next week. There is still quite a bit of uncertainty regarding the track/strength of the tropical cyclone so although the forecast does not show poor conditions at this time that could change. The best chance of tropical storm force winds looks to be along the GA coast Friday morning, especially in squalls. Cooler and drier conditions should then prevail into Monday, although a few showers can`t be ruled out mainly near the coast. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... Mainly VFR conditions to persist. There`s a chance that MVFR ceilings will develop around sunrise, potentially on and off through late morning though the chances are pretty low. Scattered showers will continue to move onshore through the morning though the low-level moisture profile hints that the chance for something to make it far enough inland to affect a terminal will be southeast GA. This afternoon, better coverage of showers and tstms expected especially once the sea breeze sets up. Maintained vicinity showers at both terminals through the afternoon. The brunt of the activity will taper off around sunset. Extended Aviation Outlook: No significant concerns, although much depends on the track/strength of Tropical Depression Nine late this week. && .MARINE... A weak coastal trough will linger through tonight with NE to E winds generally 15 kt or less. Winds will strengthen to close to 15 kt along the coast this afternoon with the sea breeze. The combination of several swell trains plus additional wind wave will yield 3-5 ft seas during the period. Tuesday through Saturday: A weak tropical cyclone is forecast by the NHC to be near the NC Outer Banks into while a weak low pressure possibly develops off the Southeast U.S. coast Tuesday night and tracks to the northeast into Thursday. Then, a tropical storm is forecast by the NHC to move northeast across northern Florida Thursday and then well off the GA/SC coasts through the rest of the week as it moves farther into the Atlantic. Tropical storm force winds are possible in the GA waters, especially beyond 20 nm, beginning Thursday night. Farther north across the SC nearshore waters only Advisory conditions are anticipated. There is still some uncertainty in this forecast so stay tuned. Rip Currents: Since we had rip current reports both Saturday and Sunday and the swell height/period continues to increase, a high risk seems warranted again today. An enhanced rip current risk will linger through much of the week due to continued long-period swells. && .TIDES/COASTAL FLOODING... Tides remain elevated due to ongoing east/northeast winds, long period swell energy and influences from the approaching new moon. The latest extratropical surge guidance suggests afternoon high tides through mid-week will be very close to levels which will produce shallow coastal flooding, especially along the lower South Carolina coast. Coastal Flood Advisories may eventually be needed. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...High Risk for Rip Currents through this evening for GAZ117-119- 139-141. SC...High Risk for Rip Currents through this evening for SCZ048>051. MARINE...None. && $$ NEAR TERM...JRL SHORT TERM...RJB LONG TERM...RJB AVIATION...JRL/RJB MARINE...JRL/RJB TIDES/COASTAL FLOODING...