textproduct: Charleston

SYNOPSIS

High pressure will extend across the region for much of the week. A cold front will push offshore Thursday morning with another cold front possibly moving south through the area over the weekend.

NEAR TERM /THROUGH TONIGHT/

Longwave trough is nicely observed on the mid and upper level GOES water vapor channels as it moves towards the east coast. With some weak positive vorticity advection alongside being in the right entrance region of the upper level jet, scattered light rain is observed on radar. Not expecting to squeeze out more than a couple hundredths, with probabilities for a tenth of an inch of QPF at or below 15% from both the HREF and REFS. Given the continuation of dreary conditions, expect afternoon highs to struggle to reach up into the lower 50s across southeast South Carolina, while those in southeast Georgia will be a touch warmer in the mid 50s.

For the late afternoon and into the overnight period, a surface low quickly forms just north of the region under a stronger shortwave, with a surface high pressure shifting behind it. This will bring an end to the light scattered rain, with a heightened surface pressure gradient resulting in slightly breezy conditions, especially along the coast where gusts into the teens are expected to continue into the overnight period. Ahead of the surface high pressure, cooler air is advected down into the region, with overnight lows in the upper 20s to lower 30s for those inland, and lower to mid 30s along the coast. Combined with the breezier winds, wind chills tonight will dip into the lower to upper 20s, just high enough to forgo any cold weather headlines at this time.

SHORT TERM /TUESDAY THROUGH THURSDAY/

The Tuesday through Thursday period will offer much improved conditions compared to the rainy and foggy weather that has been observed for the past several days. A broad west to northwest flow will dominate aloft as a large area of high pressure pressure gradually shifts offshore of the Southeast U.S. coast. A broad trough is forecast to dig across the eastern CONUS Wednesday into Thursday which will help drive a weak cold front offshore Thursday night. Moisture return ahead of the front looks meager at best with a dir airmass progged to hold over much of the Gulf. PWATs are forecast to surge somewhat right ahead of the front itself, but will remain well below the 1" mark. This lack of moisture coupled with the corridor of great quasi-geostrophic forcing progged to remain displaced well to the north, suggests the front will pass through dry with little prospects for measurable rainfall. Temperatures will moderate ahead of the front with highs reaching the upper 40s/lower 50s Tuesday and lower-mid 60s Wednesday into Thursday. Lows Wednesday morning will drop into the upper 20s well inland to the lower 40s at the beaches with upper 30s/lower 40s inland with upper 40s/near 50 at the beaches Thursday morning.

LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/

Quiet weather will generally prevail into the weekend as high pressure slides east across the Southeast U.S. and eventually offshore. A cold front is forecast to backdoor in from the north on Sunday as as the beginnings of a cold air damming/wedge take shape. There are considerable timing differences noted with the southward moving wedge front Sunday. The timing of the front will closely tied to any possible surface cyclone that develops along the front. For now, both the GFS and ECMWF ensembles, including any AI counterparts, keep any surface low weak and tracking well to the north. The area may be fully wedged in on Monday with cloudy and cool conditions prevailing. There was no reason to deviate from the 08/13z NBM at this time given the uncertainty, although NBM-based temperatures Sunday and Monday may end up being too warm depending on how the wedge evolves.

AVIATION /18Z MONDAY THROUGH SATURDAY/

18Z TAF - While there has been some temporary improvements to the flight categories across the tri-county region, MVFR to LIFR cigs will be continuing/building into the region for the remainder of the afternoon hours. As surface high pressure builds into the region this evening and overnight, the LIFR-MVFR cigs continue, though drier air mixes in and scours out the cloud coverage Tuesday morning. Winds will remain on the gusty side this later this afternoon and evening, decreasing into the morning hours on Tuesday.

Extended Aviation Outlook: There are no high confidence concerns.

MARINE

Through tonight: Northerly flow across the local waters will strengthen through the late afternoon becoming a solid 15-20 knots by sunset. Winds will strengthen further overnight through the early morning hours with increasing potential for 25 knot gusts, especially in the nearshore waters from South Santee down to Edisto Beach, SC, and the outer waters from Savannah to Altamaha Sound GA. Seas will be increasing up to 5 feet in the outer reaches of the nearshore waters from South Santee down to Edisto Beach and the outer waters from Savannah to Altamaha Sound GA late in the day. Then overnight seas will tick upward about another foot, bringing a period of 6 ft seas into the aforementioned waters. The previously issued Small Craft Advisory looks to be in good shape, so no changes were made.

Tuesday through Saturday: Winds and seas will diminish below advisory levels across the South Santee-Edisto Beach nearshore and Georgia offshore waters by mid-morning Tuesday. Otherwise, winds will turn more southerly for Wednesday and more westerly Thursday into Saturday as high pressure slides offshore and a cold front pushes offshore. Winds and seas could surge to Small Craft Advisory levels Wednesday night/Thursday morning immediately ahead and just behind the cold front. Advisories at the most likely over the South Santee-Edisto Beach and the Georgia offshore legs where the latest LREF probs for gusts >25 kt is running 50-80%. Otherwise, winds and seas will remain below Small Craft Advisory thresholds.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory from 4 PM this afternoon to 10 AM EST Tuesday for AMZ350-374.