Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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545 FXUS62 KCHS 181944 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 344 PM EDT Wed Sep 18 2024 .SYNOPSIS... Weak high pressure will develop over the region on Thursday. The area of high pressure is expected to gradually strengthen through early next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Mid level low over the Carolinas this afternoon will slowly drift eastward tonight, with the associated trough axis becoming oriented along the East Coast by around daybreak Thursday. At the surface, a weak boundary will also push east, and eventually offshore overnight. Highest coverage of showers/thunderstorms will be late this afternoon and evening then activity will largely decrease with loss of heating. However with some moisture and upper forcing lingering, a few showers could percolate overnight, especially over South Carolina. Otherwise, latest guidance hints at fog developing late towards morning particularly over southeast Georgia. Included mention of patchy fog. Lows should average in the upper 60s to lower 70s. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/... Thursday: Short term guidance indicates that the forecast area will remain under a broad H5 longwave trough. At the sfc, a weak ridge should build across the western and central Carolinas as a broad trough remains over the Coastal Plain. As temperatures warm into the mid to upper 80s, a very weak sea sea breeze is forecast to develop during the early afternoon, but should remain over the coastal counties through late afternoon. There should be enough instability during the heat of the afternoon to support isolated to scattered showers with isolated thunderstorms along the coast. Any convection should dissipated by the mid-evening hours. Friday: The axis of the mid-level trough should ripple east over the western Atlantic as strong ridge centered over TX starts to build east. GFS indicates that a short wave is expected to track from north to south across the forecast area during the afternoon. As temperatures reach the mid to upper 80s over dewpoints in the 70s, weak instability should develop across the region. The combination of the shortwave passage and weak instability may support isolated convection along the coast during the afternoon. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Saturday and Sunday, the forecast area will become dominated by weak sfc high pressure as a H5 ridge builds across the Deep South and Southeast U.S. Forecast soundings indicate that the environment will remain generally dry with a significant inversion at H75. The forecast will indicate dry conditions each day. High temperatures should favor values in the upper 80s, with low 90s possible across inland GA on Sunday. Monday through mid-week, long term guidance indicates that the H5 ridge will shift east across the northern Gulf coast and FL. H5 heights should increase across the forecast area, limiting any instability across the forecast area. The forecast will feature dry weather through early next week. High temperatures are forecast to remain in the mid to upper 80s on Monday, then mid 80s expected through the rest of the forecast period. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... Prevailing VFR through 18z Thursday, although brief flight restrictions are possible in showers and maybe a couple thunderstorms this afternoon and evening. Shower coverage will slowly diminish late evening and overnight. Towards Thursday morning, there are some indications that fog/low clouds could develop. Showed hints of this in the TAF but did not have high enough confidence to include prevailing restrictions. Extended Aviation Outlook: VFR. No significant weather expected. && .MARINE... Tonight: Southerly flow late this afternoon and early evening will veer to the west and northwest late tonight towards daybreak. Speeds generally remain less than 10 knots with seas 2 to 4 feet. Thursday through Sunday: Building high pressure should result in winds between 10-15 kts with sea generally between 2-4 ft. No headlines expected during this period. Rip Currents: The combination of a lingering swell around 2 ft at 9 seconds and high astronomical tides from the full moon will lead to a Moderate Risk of rip currents for all of our beaches today. && .TIDES/COASTAL FLOODING... Given high astronomical tides and latest tidal departures, minor coastal flooding is expected along the Charleston and Colleton county coasts with the evening high tide cycle. A Coastal Flood Advisory has been issued for 7-11 PM with tide levels expected to peak between 7.3-7.5 ft MLLW. Further south and along the Georgia coast, current forecast has tides peaking just shy of minor flooding criteria (9.5 ft MLLW in Fort Pulaski), so no advisory has been issued. Will continue to monitor trends. Positive tidal anomalies along with high astronomical tides from the full moon will lead to elevated tides for the rest of this week and through the weekend. Coastal Flood Advisories will probably be needed for both the morning and evening high tides through Friday for both Charleston Harbor and Fort Pulaski. Saturday and Sunday, the astronomical high tides start to lower but the morning high tides will likely be elevated enough to still require Coastal Flood Advisories (especially for Charleston and coastal Colleton Counties). More uncertainty exists for Fort Pulaski. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...Coastal Flood Advisory from 7 PM to 11 PM EDT this evening for SCZ049-050. MARINE...None. && $$ NEAR TERM...ETM SHORT TERM...NED LONG TERM...NED AVIATION...ETM/NED MARINE...ETM/NED