AFD_CHS

FXUS62 KCHS 032002 AFDCHS

Area Forecast Discussion National Weather Service Charleston SC 402 PM EDT Tue Jun 3 2025

.SYNOPSIS...

A coastal low will result in unsettled weather across the region late tonight through late in the week. A cold front could approach the region over the weekend into early next week.

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...

A well-defined Rex Block pattern over the Southeast U.S. should gradually break down tonight. As the blocking weakens, the H5 low should slide north over the FL Panhandle by daybreak Wednesday. At the sfc, a trough will lift north across FL, reaching the FL/GA line by daybreak Wednesday. PW values will increase from the south through tonight, with values exceeding 2 inches by late tonight. HREF indicates that SBCAPE values will increase to around 1000 J/kg across the Atlantic waters, pushing over the immediate coastal zones late tonight. Showers and thunderstorms should gradually increase in coverage across the marine zones, tracking to the NW. Using the timing of the HREF, PoPs will ramp up to categorical over waters with likely values along the coast south of the CHS Harbor, isolated to scattered values inland. Low temperatures are forecast to range from around 70 degrees inland to the low 70s along the coast.

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...

Wednesday: With strong mid-lvl ridging situated over the Eastern CONUS, a coastal low will shift off the Florida coastline in the morning. This low will then slowly drift northward up the coastline towards the region throughout the day. Tropical moisture that has already caused heavy rains across South Florida, will be ushered up with this low. The more concerning part of this is that PWAT values exceed 2+ inches tomorrow, and enhanced rainfall will rates will likely be realized within pockets of more concentrated convection. In these pockets, Flood Advisories may be needed. At this moment, rainfall values range from 1.50 to 2.50 inches across the region. It's hard to pick out a particular area that will receive the most rainfall at this time as it will depend on where exactly these thunderstorms train over. 12Z HREF suggests showers and thunderstorms entering Southeastern Georgia ~11-12Z tomorrow and slowly moving into the rest of the region throughout the day. There seems to be a little break in showers and thunderstorms the evening (23-00Z) and then ramps back up again overnight (~04Z) through Thursday morning. All deterministic models have kept the idea that numerous to widespread showers will persist across the entire area for the majority of the day, which seems to match up with what the HREF is showing. With not a lot of instability and lapse rates remaining unimpressive, the severe threat looks to be on the lower end with excessive rainfall being more of the main threat with these storms. However, with the instability being better over the waters, it is possible to see few strong storms just off the Atlantic coastline. Due to the amount of cloud cover tomorrow, temperatures were lowered a bit with highs only reaching into the upper 70s to low 80s. Lows will be mild with temperatures only dipping down to the upper 60s to low 70s.

Thursday and Friday: Depending on the forward motion of this system, this coastal low should move out of the region sometime on Thursday afternoon. However, the ECMWF has a slower progression and doesn't have the low moving out of the region until Thursday night .. but this seems to be the only outlier. Deep tropical moisture will remain in the area with PWAT values 2+ inches. Showers and thunderstorms will likely continue throughout most of the day on Thursday, until the low shifts up north. Expect PoPs to decrease overnight on Thursday into Friday morning. With the sea breeze pushing inland on Friday afternoon, this could cause for another chance of showers and thunderstorms to form. There are some hints that instability could be more than the previous days and the severe threat will be monitored in the upcoming days. Expect highs to reach into the upper 80s to low 90s for both days.

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...

With west-north-westerly flow in place Friday night, this should give a chance for the pattern to change to longwave troughing over the weekend. A cold front could potentially approach the region from the northwest over the weekend. This will create typical diurnal summertime pattern of scattered showers and thunderstorms in the afternoon. Expect temperatures to be above-normal throughout the period.

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...

18Z TAFs: Southeast winds should remain between 10 to 15 kts with some gusts in the wake of the sea breeze. Wind speeds should settle with shallower mixing early this evening. Cloud cover will increase through the night from the south, developing ahead of a coastal low. A band of showers and thunderstorms is timed to pass over KSAV between 9-12, highlighted with a TEMPO. This band may reach KCHS and KJZI between 14-18Z, highlighted with a PROB30. Shower and thunderstorm activity should trend greater through the day. In addition, IFR to MVFR ceilings may persist over KSAV through much of the daylight hours.

Extended Aviation Outlook: As the aforementioned coastal low shifts up the coastline, showers and thunderstorms could cause brief flight restrictions through the period.

.MARINE...

Tonight, as a sfc trough approaches from the south, east winds will gradually strengthen. By dawn, east winds are forecast to reach 10 to 15 kts with gusts into the low 20. As a result, seas should build from 2 to 4 ft this evening to 3 to 5 ft by late tonight. Given an area of low pressure approaching from the south, non-supercell index may develop values exceeding one unit. It is possible that the environment may support a moderate risk for waterspouts early Wednesday.

Wednesday through Saturday: With the coastal low slowly shifting northward up the coastline on Wednesday, expect westerly winds to become fairly gusty (up to 23-25 kt) beginning ~10-12Z and remain quite gusty until Thursday afternoon. Winds will shift more southerly Wednesday evening as the coastal low moves into the region. East-southerly swell will mix into the Atlantic waters and cause for some decent waves to take shape on Wednesday and Thursday. The low will then shift northwards out of the region on Thursday evening and winds will ease down a bit and become easterly for a brief moment and then switch back to southerly Saturday morning. Seas should range from 4 to 5 ft through Friday morning with 6 footers in the outer Georgia waters on Wednesday evening into early Thursday morning. Then, expect seas to back down to 2 to 3 ft for the rest of the period.

Rip Currents: Given a coastal low moving up the coastline, a Moderate risk of rip currents is expected Wednesday (tomorrow) and Thursday at all beaches.

.CHS WATCHES/WARNINGS/ADVISORIES...

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

NEAR TERM...NED SHORT TERM...Dennis LONG TERM...Dennis AVIATION...Dennis/NED MARINE...Dennis/NED