textproduct: Charleston

WHAT HAS CHANGED

Aviation section has been updated.

KEY MESSAGES

- 1) Hot and humid conditions with periods of showers and thunderstorms across SE GA/SC through Thursday. Locally heavy downpours are possible.

- 2) An unsettled wet pattern is expected to develop Friday into the weekend, increasing the potential for heavy rainfall and localized flooding.

DISCUSSION

KEY MESSAGE 1: Hot and humid conditions with periods of showers and thunderstorms across SE GA/SC through Thursday. Locally heavy downpours are possible.

The warm and moist airmass we've been experiencing the past couple days will continue to impact the area, though a pattern shift is on the way as a cold front begins to slide down towards the region throughout the day. After overnight lows in the lower to mid 70s, expect partly to mostly cloudy skies throughout the morning hours as temperatures climb, with scattered showers also starting to form as the cap erodes and convective temperatures are met.

Severe weather potential looks to remain limited given the weak shear aloft, but deep convection amidst the moist environment with PWATs remaining near 2 inches brings the risk of locally heavy rainfall. HREF probabilities indicate a 50 to 70% chance for >=1" of rainfall in 3 hours this afternoon, highest across southeast Georgia and tapering off into southeast South Carolina, with a 30% chance for >=3" of rainfall in 3 hours for portions of southeast Georgia. With westerly surface flow strengthening throughout the day, the expected sea-breeze looks to be pinned a closer to the coast today, which is where the heaviest rainfall is expected to focus. Flood Advisories or even a Flash Flood Warning could be needed where heavier storms form.

Similar to Wednesday, today is expected to be another warm and humid day as temperature climb into the upper 80s to lower 90s. Areas along the coast will see dewpoint temperatures remaining in the mid 70s, which is expected to produce heat indices just above 100 degrees for a few hours.

This evening and overnight, the weak cold front begins to meander into the region, which will continue rainfall chances into the overnight hours given the provided lift. The cooler air doesn't filter in behind the front just yet, so expect overnight lows to remain in the upper 60s to mid 70s across the region.

KEY MESSAGE 2: An unsettled wet pattern is expected to develop Friday into the weekend, increasing the potential for heavy rainfall and localized flooding.

On Friday, a cold front is forecast to slow as it pushes over the Savannah River, expected to become stationary over SE GA Friday afternoon. At H5, a broad weaknesses will develop over the Southeast U.S. as the region remains longwave progresses across New England and a 590 dm ridge is centered over Cuba. Using a blend of MOS, high temperatures are forecast to range in the mid 80s, with dewpoints around 70 degrees. The warm and moist conditions under the broad mid- level weakness will produce a large field of SBCAPE between 1000- 1500 J/kg. In addition, guidance indicates that PW values along and south of stationary front should range around 2" with values between 1.7" to 1.9" across the SC Lowcountry.

NAM12 indicates that high pressure may surge SW as the ridge becomes blocked by the Southern Appalachians Friday afternoon. Deep moisture convergence will likely develop along the NW to SE oriented front across SE GA. High resolution guidance indicates that showers and thunderstorms will rapidly develop across SE GA from late morning through the afternoon hours. The convection will develop within an area of tropical PW with RH between 850-300 mb near 90%, likely producing periods of torrential downpours. The 0Z HREF highlights SE GA with a 90% of 1"/3hr and a large area of 50% for 3"/hr for Friday afternoon. Given the recent wet weather, these rainfall rates could become excessive, producing localized pockets of flooding or flash flooding.

Friday night, H5 heights across the forecast will become zonal, with a shortwave rippling across the CWA overnight. Guidance, including GFS and ECMWF based AI models, indicate a deepening sfc trough or wave along the stationary front. Convection coverage should concentrate within the trough or wave over the SC Lowcountry on Saturday, then tracking offshore Saturday night. On Sunday, the center of a sfc high is forecast to become centered off the coast of the mid-Atlantic states. The sfc ridge should increase across the CWA on Sunday, resulting in widespread isentropic lift through the day.

The wet pattern is expected to persist through at least early next week. Temperatures should cool through this weekend, with highs in the upper 70s to around 80 for Sunday and Monday. Lows in the 60s on Sunday and Monday.

AVIATION /12Z THURSDAY THROUGH MONDAY/

12Z TAFs - As expected, very scattered ground fog is observed across portions of the area, with some near MVFR cigs occuring as well. As the morning progresses, expect the fog to dissipate and ceilings to rise. By late morning/early afternoon, a round of scattered showers and thunderstorms is expected to get started. Latest trends continue to favor southeast Georgia for seeing rainfall first, but have kept PROB30s going at all terminals with SAV seeing their start at 20Z and CHS/JZI shortly after. A cold front begins to meander into the region this evening and overnight, which may again bring a round of showers and thunderstorms along with it. Patchy fog may form overnight for areas that see heavy rainfall today.

Extended Aviation Outlook: More periodic flight restrictions are possible Friday into the weekend as the potential for widespread showers/thunderstorms increases. In addition, patchy overnight fog and/or stratus cannot be ruled out after recent rains.

MARINE

Today and Tonight: As a surface high pressure remains off to our east throughout the day, winds will remain out of the southeast at 10-15 knots with a few gusts to 20 knots possible. In addition, scattered shower and thunderstorms are expected to develop later this morning with chances continuing into the evening and overnight hours as a weak cold front begins to slide into the region.

Friday through Monday: On Friday, ENE winds may surge as the cold front pushes across the SC waters, with gusts approaching 25 kts. It is expected that gusts will remain just below Small Craft Advisory criteria on Friday. However, wave heights should build through the day, reaching 3-5 ft by Friday afternoon. The pressure gradient may lessen on Friday night into Saturday as a frontal wave develops over the marine zones. However, as the wave slides east on Sunday, high pressure will surge south across the coastal waters, pinching the pressure gradient. As a result, ENE winds will strengthen on Sunday, with gusts approaching gales during the daylight hours. Wave heights are forecast to build over 6 ft on Sunday, the receding below 6 ft Sunday night. A weaker pressure gradient should develop on Monday, yielding improving wind and sea conditions.

Rip Currents: An elevated rip current risk will remain through the week with a modest easterly swell around 3 to 4 feet every 8 seconds and sea breeze influences. A moderate risk of rip currents is in place for all area beaches through Friday.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...None.