Marine Weather and Tide Forecast for Sullivan's Island, SC

KEY MESSAGES
- 1) Showers and thunderstorms will continue to impact portions of Southeast Georgia and Southeast South Carolina each day through the upcoming weekend.

- 2) The potential for coastal flooding will persist into Friday, primarily for coastal portions of Charleston and Berkeley Counties.

DISCUSSION
KEY MESSAGE 1: Showers and thunderstorms will continue to impact portions of Southeast Georgia and Southeast South Carolina each day through the upcoming weekend.

Tonight: The risk for showers/tstms will gradually lower this evening with the loss of daytime heating, keeping most areas dry for several hours during the overnight period. The exception could be across far southern GA zones where a cluster of shower/thunderstorm activity tries to nudge north across the Altamaha River prior to waning late evening. Late tonight, weak warm air advection and isentropic ascent could spark off a few nocturnal showers prior to daybreak, mainly across the Lowcountry. Some marine-based convection could also brush coastal areas with the bulk of the activity remaining over the coastal waters, especially near the west wall of the Gulf Stream.

Friday through the Weekend: On Friday the upper level pattern will begin to shift as the subtropical high pressure over the western Atlantic shifts eastward. To the west a short wave trough aloft will slowly progress east from Saturday into Sunday. The southwesterly flow aloft will allow for efficient moisture advection into the region, with PWATs forecast to increase to 2+ inches Saturday. Coverage of showers and thunderstorms on Friday will be isolated to scattered at best as the synoptic pattern begins to shift. Greater coverage of precipitation is forecast on Saturday and the forecast features numerous to widespread showers and storms. While a strong to marginally severe thunderstorm cannot be ruled out, ML CAPE values are forecast to be up around 2000 J/kg, heavy rainfall is the main hazard through the weekend. Very weak storm motions could result in localized heavy rainfall, leading to minor flooding issues within low-lying and poor drainage areas.

KEY MESSAGE 2: The potential for coastal flooding will persist into Friday, primarily for coastal portions of Charleston and Berkeley Counties.

Tides in the Charleston Harbor are expected to peak 7.1-7.3 ft MLLW with the evening high tide. This will result in minor salt water flooding across coastal portions of Charleston and Colleton Counties, where a Coastal Flood Advisory remains in effect until 10 PM this evening. Diminishing departures should keep tide levels with high tide Friday evening from reaching 7.0 ft MLLW, although it could be close. The current total water forecast keeps the tide peaking at 6.9 ft MLLW, but further refinements may be needed.

AVIATION /00Z FRIDAY THROUGH TUESDAY/
VFR conditions should generally prevail overnight and into early daylight hours Friday. However, brief flight restrictions are possible at CHS with lower cigs late. Shallow ground fog could also result in reduced vsbys at times within a few hours prior to and around daybreak Friday. Attention then turns over to convection developing at all terminals mid-late morning Friday and persisting into afternoon hours. PROB30 groups for thunderstorms and MVFR conditions have been introduced at JZI from 13-19Z Friday, at CHS from 13-19Z Friday and at SAV from 18-22Z Friday.

Extended Aviation Outlook: Periodic flight restrictions will be possible each day through the weekend within showers and thunderstorms, mainly during the afternoon hours.

MARINE
Through Tonight: Conditions are expected to remain well below Small Craft Advisory levels through the overnight period. In general, southerly winds around 10 kt will persist with seas ranging between 2-3 ft.

Friday through Monday: Generally tranquil marine conditions should continue on Friday through early next week, with winds mostly 5 to 10 kts as high pressure remains the dominant feature across the Atlantic. Southwest winds are expected on Friday, becoming more southerly to southwesterly through the weekend before turning westerly around 5 kts on Monday. The main concern for mariners will be scattered showers and thunderstorms, with the greatest coverage likely Friday afternoon through Saturday and additional storms possible on Sunday and Monday. Any stronger storm could produce frequent lightning, heavy rain with reduced visibility, and brief gusts well above prevailing winds. Seas will range from 2-3 ft through the period.

CHS WATCHES/WARNINGS/ADVISORIES
GA...None.
SC...Coastal Flood Advisory until 10 PM EDT this evening for SCZ149- 150.
MARINE...None.