textproduct: Charleston

WHAT HAS CHANGED

The Aviation section has been updated for the 00z TAF issuance.

KEY MESSAGES

- 1) Hot and humid conditions with periods of showers and thunderstorms across SE GA/SC through Thursday. Locally heavy downpours are possible.

- 2) An unsettled wet pattern is expected to develop Friday into the weekend, increasing the potential for heavy rainfall and localized flooding.

DISCUSSION

KEY MESSAGE 1: Hot and humid conditions with periods of showers and thunderstorms across SE GA/SC through Thursday. Locally heavy downpours are possible.

A warm and moist airmass will remain in place through Thursday as deep moisture continues to advect northward along the western periphery of Atlantic high pressure. With PWATs increasing to around 2 inches, scattered to numerous showers and thunderstorms will initiate along and west of the sea breeze during the mid to late afternoon hours. The upper ridge in the Atlantic will help to suppress convection, mainly along the coast. However, a slightly weaker ridge Thursday could allow for more robust development and coverage. Additionally, a weak cold front will begin to drop southward toward the forecast area Thursday providing additional source of lift.

While severe potential should remain limited, deeper convection could produce heavy downpours dropping a quick inch or two, and possibly isolated minor flooding. HREF probabilities indicate a 20-40% chance for 1" or greater rainfall from these storms through this evening, with chances increasing to 40-70% for Thursday. Flood Advisories or even a Flash Flood Warning could be needed where heavier storms track over the same area; the greater chances occurring Thursday.

Humidity may range a bit higher on Thursday as the upper ridge weakens and the area of rain soaked ground increases. Given high temperatures in upper 80s to around 90 and dewpoints in the low to mid 70s, conditions will remain hot and humid. Coastal counties could see heat index values between 100 to 103 degrees.

KEY MESSAGE 2: An unsettled wet pattern is expected to develop Friday into the weekend, increasing the potential for heavy rainfall and localized flooding.

As noted in days past, will see a sfc cold front stall near the region Friday, resulting in a prolonged period of unsettled weather. While showers and perhaps a few storms may be ongoing by Friday morning, expect coverage to become more widespread during the afternoon and evening hours. This pattern will continue into Saturday and Sunday as the aforementioned front and sfc low lingers along the coast.

Given the stationary nature of the front, combined with slow storm motion (10-15 kt), do want to emphasize that any storm may be capable of producing locally heavy rainfall - especially as PWATs near 2 inches. In terms of accumulations, latest guidance still maintains anywhere from 2 to 4 inches over a 72 hour period spanning Friday through Sunday. However, there has been a subtle shift southward in the axis of higher accumulations. Though this axis could still shift more in the coming forecast cycles, do think it's a trend worth keeping an eye on. In regard to severe weather, latest soundings do show ample lift and moisture - however, with shear remaining meager, think our chances for seeing severe storms will be rather limited.

Otherwise, look for afternoon highs in the low to mid 80s to become common, with overnight lows falling into the 60s.

AVIATION /00Z THURSDAY THROUGH MONDAY/

The 00z TAF period begins with VFR conditions at KCHS, KJZI, and KSAV. Late tonight, there is potential for fog to develop around KSAV resulting from the thunderstorm activity that impacted the area this afternoon. Then, MVFR ceilings will again be possible at all 3 TAF sites from around sunrise through mid morning with the onset of surface heating and development of the cumulus and stratocumulus field. Attention then turns to afternoon and evening thunderstorm potential. Current model guidance suggests that the best potential will be around KCHS and KJZI beginning around 19-20z and continuing for a few hours. We have introduced PROB30 groups to account for this potential.

Extended Aviation Outlook: Brief flight restrictions possible within showers and thunderstorms at CHS/JZI/SAV terminals during the afternoon hours into the later half of the week. More periodic flight restrictions are possible Friday into the weekend as the potential for widespread showers/thunderstorms increases. In addition, patchy overnight fog and/or stratus cannot be ruled out after recent rains.

MARINE

Tonight: The marine zones will remain under the influence of broad high pressure. South winds should remain between 10-15 kt with gusts up to 20 kt. Wave heights will range between 3-5 ft.

Thursday through Sunday: Conditions are generally forecast to remain below Small Craft Advisory criteria into the weekend, with daily chances for showers and thunderstorms. A surface front pushes down into the region overnight into Friday, with a surge in winds 15 to 20 knots behind the front Friday afternoon before the front stalls. The surface front lingers across the region throughout the weekend, and a surface low pressure or two may form along the front, possibly pinching the pressure gradient a couple times throughout the weekend. This would bring brief periods periods of Small Craft Advisory level winds and seas, though confidence in timing and location are currently low.

Rip Currents: An elevated rip current risk will remain through the week with a modest easterly swell around 3 to 4 feet every 8 seconds and sea breeze influences. A moderate risk of rip currents is in place for all area beaches through Thursday.

CHS WATCHES/WARNINGS/ADVISORIES

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