Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
644 FXUS62 KCHS 100941 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 541 AM EDT Sun Aug 10 2025 .SYNOPSIS... A stationary front will linger south of the area through early this week, while high pressure remains centered well to our north. && .NEAR TERM /THROUGH TONIGHT/... Bands of heavy rain continue to move onshore early this morning, mainly along the lower South Carolina coast. Pops were nudged up to 100% with these bands. A near term flash flood risk could setup between Charleston and Savannah through daybreak. Rainfall rates as high as 2-3 in/hr have been observed around Hilton Head and could reach as high as 3-4 in/hr at times. The synoptic pattern has changed little during the past 24 hours. The region remains positioned beneath a large mid-level weakness with a nearly continuous stream of vorticity crossing the area as impulses round the periphery of the subtropical anticyclone centered well offshore. The atmosphere will remain extremely moist into tonight with PWATs progged to approach 2.5-2.6" at times. MLCAPE will also remain modest through the period, peaking during the afternoon hours. As impulses move through, waves/bands of showers/tstms will continue to develop and push inland throughout the day. This convective pattern will continue into tonight with most of the activity refocusing back over the Atlantic and across the coastal counties during the early morning hours Monday. The mean steering flow does look a bit stronger than what was experienced Saturday, but the wind flow will likely support convective training where clusters of showers/tstms form. Intense hourly rainfall rates are likely given PWATs will surge above 2.5" at times. These rates could exceed 3 in/hr at times. This combined with warm cloud processes, higher mixed-layer instability and wet ground conditions, will support an elevated potential for scattered instances of flash flooding through tonight. 10/00z HREF 6-hr probabilities for >5" are maxing out at about 20-40% in spots through tonight, suggesting localized amounts in excess of 5" could occur with a larger, more general 1-3" spread. Given the very wet antecedent conditions that are in place, a Flood Watch as been issued for areas roughly along/east of I-95 to address the elevated risk for scattered urban and flash flooding. This includes both the Charleston and Savannah Metro Area. Pops will range 80-100% today with 70-90% tonight, highest at the coast. Highs today will range from the upper 70s/lower 80s, except lower-mid 80s south of I-16. && .SHORT TERM /MONDAY THROUGH WEDNESDAY/... Monday: High pressure just offshore of New England will once again create a wedge of high pressure along the eastern side of the Appalachian Mountains. Just to the south a stationary front will remain stalled near the Florida/Georgia border. High pressure aloft will prevail over Bermuda, with the western periphery over the local forecast area. The moist and unstable environment observed over the weekend will persist into Monday. Models are showing PWATs 2.2-2.4" and CAPE values around 1500 J/kg, supportive of numerous to widespread showers and a few thunderstorms. The severe thunderstorm threat remains low, with the main hazard remaining locally heavy rainfall. A Flood Watch is in effect for counties roughly along and east of I-95 through 6 AM Monday morning. This Flood Watch may need to be extended into Monday depending on how trends progress. Temperatures will remain several degrees below normal, with high temperatures in the low to mid 80s. Tuesday and Wednesday: The wedge of high pressure at the surface will begin to break down on Tuesday as high pressure develops over the Carolinas. Ridging aloft will continue to build into the region. With high pressure dominating at the surface and aloft the region will see a pattern shift back towards a more typical-summertime pattern. Temperatures will return to near normal, with heat index values approaching triple digits on Wednesday. Scattered to numerous showers and thunderstorms will be possible each afternoon, mainly diurnally driven by the afternoon sea breeze. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... High pressure will dominate at the surface and aloft through the end of the week and into the weekend. As the high pressure strengthens temperatures will increase, reaching the low to mid 90s by Thursday. This pattern should yield a typical summer-time pattern with afternoon thunderstorms and hot and humid conditions making a return. Heat index values will return to triple digits, with 100- 105F in the forecast, shy of Heat Advisory criteria. && .AVIATION /10Z SUNDAY THROUGH THURSDAY/... 10/12Z TAF Discussion: KCHS/KJZI/KSAV: Waves/bands of showers with embedded tstms will occasionally impact the terminals through tonight. Timing is highly uncertain given showers/tstms could pop just about anywhere at anytime given the very moist conditions that are in place. Several bands could reach KSAV by mid-morning and KCHS/KJZI by mid-late morning. Brief instances of IFR vsbys/cigs could occur with this activity. Extended Aviation Outlook: Brief flight restrictions will be possible through the weekend and into early next week with afternoon showers/thunderstorms. && .MARINE... Through Tonight: There are no real concerns through tonight. Easterly winds will prevail with winds around 15 kt. Seas 2-4 ft. Vsbys in showers/tstms could drop below 1 NM at times. Monday through Friday: High pressure will prevail to the north on Monday, with high pressure then developing over the local waters through the remainder of the week. The forecast features winds SE/S around 10 to 15 knots. Some gusts could approach 20 knots along the coastline due to the afternoon sea breeze. Seas should average 2 to 3 ft. && .TIDES/COASTAL FLOODING... The recent full moon (8/9) and upcoming lunar perigee (8/14), will cause increasing astronomical tide values in the coming days. In the Charleston Harbor, high tide is expected to peak around 7 ft MLLW each evening through Monday. Coastal Flood Advisories could be needed for Charleston and coastal Colleton counties. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Flood Watch through late tonight for GAZ101-116>119-138>141. SC...Flood Watch through late tonight for SCZ042>045-047>052. MARINE...None. && $$