Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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692 FXUS62 KCHS 182224 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 624 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/... The coverage of showers will gradually diminish over the next few hours as instability wanes. An isolated rumble or two could occur, but overall the risk for tstms through this evening is low. Skies will gradually clear as convective debris thins. As the boundary layer decouples and cloud cover diminishes, the risk for fog and stratus will increase, especially where rain fell earlier in the day. The lowest 1000 hPa condensation pressure deficits look to occur south of I-16 and up through parts of Bulloch and Candler Counties. The fog qualifier was nudged higher from "patchy" to "areas of" in many of these areas. Locally dense fog with vsbys 1/4 mile or less could occur. Lows tonight will range from the upper 60s inland to the lower 70s at the beaches and Downtown Charleston. && .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 Wednesday: 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 /22Z WEDNESDAY THROUGH MONDAY/... 19/00z TAF Discussion: KCHS/KSAV/KJZI: There is a risk for fog and stratus development overnight as wet grounds from earlier rainfall combine with clearing skies and light winds. The best fog/stratus parameters look to occur across interior Southeast Georgia where KSAV will likely be found on the eastern periphery. For now, cigs were limited to MVFR with a TEMPO group from 10-13z for IFR cigs just above alternate minimums with MVFR vsbys. Lower conditions could occur pending additional model data. For KCHS, fog/stratus looks a bit more marginal although it is located close to where heavier rains fell earlier. VFR was maintained, but a TEMPO group for MVFR cigs with scattered clouds at 600 ft was introduced 10-13z to trend. Light VFR fog was also maintained 09-13z. At KJZI, VFR was continued as fog/stratus looks to remain west of the terminal. Some light fog could occur as winds go light and skies clear, but no meaningful reductions in vsbys are expected at this time. Extended Aviation Outlook: VFR. No significant weather expected. && .MARINE... Tonight: Southerly flow early evening will veer to the west and northwest late tonight towards daybreak. Speeds generally remain less than 10 knots with seas 1 to 3 ft nearshore waters out 20 NM and 3-4 feet over the Georgia offshore waters out 20-60 NM. 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. && .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. The astronomical high tides start to lower Saturday and Sunday, 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 until 11 PM EDT this evening for SCZ049- 050. MARINE...None. && $$