textproduct: Charleston

WHAT HAS CHANGED

All sections updated.

KEY MESSAGES

- 1) The risk for showers and thunderstorms will continue through the weekend.

DISCUSSION

KEY MESSAGE 1: The risk for showers and thunderstorms will continue through the weekend.

Rest of Today: A shortwave trough aloft can be seen in mid-level water vapor satellite imagery trekking eastward towards the local forecast area. Showers and thunderstorms have begun to develop, mainly across southeastern GA. Coverage will continue to spread across the region as outflow boundaries interact with each other and the sea breeze. This morning's 12Z KCHS RAOB Sounding showed a PWAT value of 2.23" points to a threat of heavy rainfall this afternoon. SPC mesoanalysis shows DCAPE values of only around 600 J/kg, limiting the overall severe weather threat this afternoon. Showers and storms will wane with nightfall.

Sunday: The mid-levels will consist of a weak trough moving over our area in the morning, then offshore during the afternoon. The surface pattern will be rather diffuse, with either a weak front well to our north or weak surface troughing over the Southeast U.S. Southwesterly flow will cause deep moisture to be over our area in the morning. PWATs should easily be above 2". This is well above normal per CHS sounding climatology and about 2 standard deviations per NAEFs. However, lower PWATs will build in from the west during the afternoon, keeping the highest PWATs along the immediate coast, before they are pushed offshore in the evening. Most CAMs point to scattered coverage forming near the coast in the afternoon, then shifting offshore and dissipating in the evening. High temperatures will be a few degrees above normal, leading to modest instability. Additionally, higher DCAPEs build in from the west during the afternoon. So while we're not expecting widespread severe weather, there could be a few hour window where strong to marginally severe thunderstorms cannot be ruled out along the coast. Locally heavy rainfall will also be possible. But the steering level winds may be just strong enough to limit significant flooding.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

A TEMPO group has been introduced at KCHS/KJZI/KSAV with the 18Z TAFs to account for afternoon showers and thunderstorms. Thereafter, prevailing VFR through the remainder of the 18Z TAF period.

Extended Aviation Outlook: Periodic flight restrictions will be possible Sunday afternoon due to showers and thunderstorms. Drier conditions return on Monday, possibly persisting through Wednesday.

MARINE

Today and tonight: The pressure pattern will generally support south- southwest winds between 10 to 15 kts across the marine zones. Wave heights are forecast to remain between 2 to 3 ft.

Through Thursday: Weak surface troughing inland will maintain generally south to southwest winds through early next week. Speeds should average 10-15 knots with seas 2-3 feet. The main time period of concern will be Tuesday and Wednesday as high pressure ridges south into the region and winds turn northeast and strengthen. Gusts in the 25-30 knot range and 4-8 foot seas appear likely for most of the waters, and Small Craft Advisories will be possible. The pressure gradient should ease on Thursday with conditions falling below advisory levels.

Coastal Flooding: Minor coastal flooding is possible with the Tuesday mid-day high tide along the Charleston and Colleton County coasts. Strengthening northeast winds are expected on Tuesday which will increase tidal departures. The tide would need ~1 ft departure to reach minor flooding thresholds of 7 ft MLLW in the Charleston Harbor. Most guidance indicates tide levels could fall right around there. A Coastal Flood Advisory could be needed. No issues expected further south along the lower SC and southeast GA coasts.

CHS WATCHES/WARNINGS/ADVISORIES

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