Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 081730 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 130 PM EDT Sat May 8 2021 .SYNOPSIS... High pressure will prevail through the weekend. Low pressure and a cold front will approach the region early week, then linger through mid-week. High pressure will build into the region by late week. && .NEAR TERM /THROUGH TONIGHT/... High pressure initially over Alabama, Georgia and the Florida panhandle will drop southeast and split into two separate regions this afternoon. One center will be found in the northeast Gulf of Mexico, while the another high forms over the nearby Atlantic. Meanwhile, a cold front will linger off to the northwest. With full sunshine, a west to northwest downslope flow in the boundary layer and warm 850 mb temperatures, we expect a large diurnal rise in temperatures. Our latest forecast shows max temperatures in the upper 70s and lower 80s most communities away from the coast. The resultant sea breeze will form during the early afternoon, and hold shoreline locations down in the lower and middle 70s. Deep mixing and some enhancement to the pressure gradient will lead to gusty afternoon winds, especially over locations east of I-95 from the Savannah area north to Beaufort, Walterboro, Charleston, Summerville and Moncks Corner. It won`t be anywhere near as strong as the winds from yesterday, but still enough to get westerly winds up near 20 mph at times prior to the sea breeze backing winds around to the south and southwest. Tonight: High pressure over the Atlantic will become the parent high, as it tracks further into the ocean. Winds will decouple in most places with sunset, and even though dew points will be increasing as the synoptic flow becomes south-southwest, conditions again favor good radiational cooling away from the coast. It won`t be as cool as this morning was, but still looking at min temperatures in the lower and middle 50s inland from US-17, with 60-65F along the barrier islands, in the Charleston metro and near the edges of Lake Moultrie. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... Sunday: High pressure will shift further south as low pressure and an associated cold front approach the region from the west. With a tight pressure gradient, winds will be quite breezy. Though, another rain-free day is expected. The area will be in the warm sector and high temperatures will be in the mid to upper 80s inland and low 80s just along the coast. Overnight Sunday, radiational cooling will be less than ideal as cloud cover increases and winds remain somewhat breezy. Low temperatures will be in the low to mid 60s inland with upper 60s to low 70s along the coast. Monday: A cold will sweep through the area on Monday before departing offshore overnight. There are some inconsistencies within the models of how much rain will actually occur across the area and the timing. The best chances for rain remains over SE GA, though could see a few showers across the SE SC as well. While the best instability will be over the waters, there could be pockets of 700- 800 J/kg of SBCAPE. Therefore, have maintained mention of thunderstorms. With sufficient shear, thunderstorms could become organized and a few stronger storms will be possible. Another day of 80s is expected with lows in the 60s. Tuesday: Another day of unsettled weather is possible as the cold front sinks south before stalling across the waters and northern Florida. Isentropic lift and PWATs around an inch and a half will support scattered showers and thunderstorms. Otherwise, high temperatures will be in mid to upper 70s across portions of SE SC and low to mid 80s across SE GA. Lows will be in the mid to upper 50s inland and low 60s along the coast and in far SE GA. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... The weather will remain somewhat unsettled through late week as a stationary front lingers in the vicinity, shortwave energy moves through the area and high pressure prevails to the north. Showers and thunderstorms will be possible on Wednesday and Thursday. While at this time, the instability is quite limited, if the stationary front lifts north, there could be a few stronger storms, mainly on Thursday. High pressure should then build into the area on Friday. Cooler temperatures are expected on Wednesday and Thursday, then a warming trend will occur. Low temperatures will mostly be in the 50s. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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18Z TAFs: VFR. Gusty W winds are expected at KCHS until sunset. Extended Aviation Outlook: VFR to prevail with gusty winds during the daylight hours Sunday and Monday. Thereafter, a cold front could bring flight restrictions to both terminals due to low clouds and showers/thunderstorms starting Monday afternoon.
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&& .MARINE... Today through tonight: While a cold front will remain off to the distant northwest, high pressure that originally is over the Southeast will reform over the Atlantic this afternoon. That high will expand tonight as its associated ridge axis sets up from east to west across southern Georgia and northern Florida. Winds will become S and SW with sea breeze influences this afternoon. For the most part winds will be at or below 15 kt, but some gusts will reach around 20-25 kt in Charleston Harbor and on the Charleston County Atlantic waters late in the day into the evening. However, the frequency and coverage of any 25 kt winds will be limited enough where we don`t anticipate a Small Craft Advisory. Seas of 2 to 3 ft will be common throughout tonight, except for several hours of 4 foot seas reaching in the AMZ350 waters later today and early tonight when winds will be their strongest. Sunday through Thursday: As high pressure departs offshore and a cold front approaches the region on Sunday, the pressure gradient will tighten and winds will increase. Small Craft Advisories could be needed for all waters, including the Charleston Harbor through early Monday. Thereafter, winds will remain around 10-15 knots on Tuesday and Wednesday. On Thursday, another round of Small Craft Advisories could be needed for winds and seas. Showers and thunderstorms will also be possible each day, with the exception of a rain-free day expected on Sunday. && .FIRE WEATHER...
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Relative humidity will fall to around 20 to 25 percent most places this afternoon, prior to the passage of the sea breeze during the early and mid afternoon. This occurs with mainly west winds that reach around 15 or 20 mph, and highest near and east of I-95 from Chatham County to Charleston and Berkeley County. As a result of these conditions, we have a Fire Danger Statement until 7 PM. Once the sea breeze develops and spreads slowly inland, relative humidity values will increase as winds become south or southwest along and near the coast. Locations outside of where we have the Fire Danger Statement today will have similar relative humidity levels, but winds will be quite a bit less. For Sunday afternoon, relative humidity will fall to 25 to 30 percent, while south and southwest wind gusts will reach 20 to 25 mph. This will support the requirement for either another Fire Danger Statement, or maybe even a Fire Weather Watch and/or a Red Flag Warning, and would cover most if not all counties.
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&& .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE... FIRE WEATHER... is the U.S. government's official web portal to all federal, state and local government web resources and services.