textproduct: Charleston

WHAT HAS CHANGED

Key Message 1 and the Aviation section was updated.

KEY MESSAGES

- 1) Locally heavy rainfall will remain a threat for portions of southeast Georgia and southeast South Carolina through Tuesday.

- 2) Minor coastal flooding is possible along the Charleston and Colleton County coastline with the Tuesday evening high tide.

DISCUSSION

KEY MESSAGE 1: Locally heavy rainfall will remain a threat for portions of southeast Georgia and southeast South Carolina through Tuesday.

Rest of Tonight: Areas of convection continue to fire in the vicinity of a weak sea breeze/outflow composite boundary that pushed west through the Charleston Tri-County and into parts of Colleton and Beaufort County. KCLX shows another round of convection moving south/southeast across the eastern Midlands and western Pee Dee. This activity will push into the Charleston Tri-County and possibly Colleton County by mid-evening, bringing additional rainfall to the area. Despite earlier convection, there is still a fair amount of MLCAPE in place, so this activity could hold together before slowly weakening as it approaches the coast. Gusty winds, locally heavy rainfall and isolated flooding remain the primary concerns.

Later tonight, there are signals that convection may re-fire over the western Midlands along an outflow being generated by convection moving east of Columbia. If it forms, it would drop south/southeast into interior Southeast Georgia and possibly parts of the Lowcountry. Confidence is only moderate at best if this area will develop. Again, gusty winds, locally heavy rainfall and isolated flooding would be the main issue.

Tuesday: A cold front will sink south of the area on Tuesday, as high pressure builds in from the north. Aloft, a mid level trough will extend into the Southeast with a shortwave rounding the base later in the day. Guidance is still a bit mixed on convective activity, but we should see at least scattered showers and thunderstorms during the first part of the day before drier air works in from the north and activity eventually pushes south of the Altamaha River. There could be pockets of heavier rainfall, but the flooding threat looks low and focused more to the south.

KEY MESSAGE 2: Minor coastal flooding is possible along the Charleston and Colleton County coastline with the Tuesday evening high tide.

Gusty northeast winds will develop along the southeast SC coast on Tuesday behind a passing cold front. This northeast flow will produce a surge in tide levels, especially around the time of the Tuesday evening high tide (occurring around 1015 PM). The astronomical tide level is 5.5 ft MLLW, so it would require a rather anomalous 1.5 ft departure to reach the minor coastal flood threshold of 7 ft MLLW. For context, historical analysis shows that a departure of 1.5 ft or higher has only occurred with ~7% of all minor coastal flood events on record. Still, minor coastal flooding is possible, and a Coastal Flood Advisory could be needed for the Charleston and Colleton county coasts.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

02/00z TAF Discussion: KCHS/KJZI: Risk for shower impacts will linger through for much of the evening hours. A cluster of storms moving across the eastern Midlands will make a run for both terminals by 01-03z. TEMPO groups for MVFR conditions were introduced to account for this. A few tstms have been observed at times, but as the atmosphere slowly stabilizes ahead of the activity, the risk for a mention of tstms is too low to justify a mention at this time. Another round of convection could develop over the western Midlands and move southeast. Much of this should remain to the west, but a PROB30 group for MVFR vsbys in RA was included 05-08z. A cold front should push through the terminals before daybreak with a period of IFR cigs possible, especially at KCHS. IFR cigs should lift to MVFR by mid-morning and linger through the day at both terminals as east to northeast winds become a bit gusty.

KSAV: VFR this evening. There are signals that a cluster of showers/tstms could develop across the western Midlands along outflow from storms near Columbia. It is uncertain if this activity will develop, but it could make a run for KSAV early Tuesday morning if it does. Fro now a PROB30 group for MVFR conditions in TSRA was included 06-09z to account for this. Otherwise, a cold front will cross the terminal before daybreak Tuesday. MVFR cigs are expected to filter in behind the front and linger through the day as east to northeast winds become a bit gusty.

Extended Aviation Outlook: Periodic flight restrictions are possible through Tuesday due to scattered showers and isolated thunderstorms. Patchy overnight fog and/or low stratus are also possible.

MARINE

Tonight through Saturday: No hazardous weather is expected across the waters tonight. The time period of most concern is Tuesday into Wednesday. High pressure will build south into the region, leading to increasing northeast winds and seas. Solid Small Craft Advisory conditions are expected across all waters. There is even a period where gusts could approach gale force late Tuesday night into Wednesday, particularly in the outer waters beyond 20 nm, but this threat looks too marginal for any Gale Watches at this point. While winds will begin to subside Wednesday night into Thursday, 6 ft seas could maintain Advisories for portions of the waters into at least part of the day Thursday. No concerns for Friday and Saturday.

Rip Currents: Gusty northeast winds and increasing swell will lead to an enhanced risk of rip currents through mid week. A Moderate Risk is forecast at all area beaches for Tuesday. On Wednesday, the forecast features a Moderate Risk across SC beaches and a High Risk at GA beaches.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory from noon Tuesday to 5 AM EDT Thursday for AMZ360. Small Craft Advisory from 3 PM Tuesday to 5 AM EDT Thursday for AMZ362. Small Craft Advisory from 5 PM Tuesday to 11 AM EDT Thursday for AMZ364. Small Craft Advisory from 5 PM Tuesday to 8 PM EDT Thursday for AMZ384.