textproduct: Charleston

WHAT HAS CHANGED

All Key Messages, sections and subsections were updated.

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.

This Afternoon/Tonight: The risk for showers/tstms will gradually shift inland through the afternoon/evening as the sea breeze matures and propagates to the west. Convection will be mostly airmass driven in the absence of any meaningful forcing mechanisms. A few stronger cells could certainly occur where updrafts can become enhanced in the vicinity of mesoscale boundary collisions with gusty winds, locally heavy rainfall and cloud-to-ground lightning being the primary hazards. Rain chances should generally end with the passage of the sea breeze. Later tonight, weak warm air advection/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 through the night 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 7.0-7.2 ft MLLW with the evening high tide. This will result in minor salt water flooding across coastal portions of Charleston and Colleton Counties and a Coastal Flood Advisory has been issued from 7-10 PM. 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 /18Z THURSDAY THROUGH MONDAY/

10/18z TAFs: KCHS/KJZI/KSAV: Risk for shower/tstm impacts look greatest at KCHS through about 20z ahead of the sea breeze. A TEMPO group for 4SM SHRA was highlighted to reflect this. Some activity may also be near KSAV through about 21z, but the bulk of this should remain west of that terminal. VCSH was used through 21z to highlight this. Activity should remain well to the west of KJZI since that terminal will be well behind the sea breeze. Overnight, there are some signals that some low status, may be some light fog, could impact inland Southeast South Carolina. Some of this may brush KCHS prior to daybreak. Some very light shallow ground fog with a scattered deck at 500 ft was included at KCHS to trend.

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: Southerly winds around 10 kt will persist with seas 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.

Rip Currents: Lifeguard groups have not reported any rip currents so far today and beach webcams suggest suggest little, if any, meaningful swell is reaching the surf zone with glassy conditions. The rip current risk has been lowered from moderate to low for all beaches for the remainder of the afternoon. The rip risk will remain low for both Friday and Saturday.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...Coastal Flood Advisory from 7 PM to 10 PM EDT this evening for SCZ149-150. MARINE...None.