textproduct: Charleston

WHAT HAS CHANGED

Updated Key Message 1 and the Aviation section for the 0Z TAFS.

KEY MESSAGES

- 1) Strong to severe thunderstorms possible this evening and again late tonight.

- 2) A more typical summertime pattern is expected for the weekend into next week with daily shower and thunderstorm chances. Hot and humid conditions are expected Monday and Tuesday.

DISCUSSION

KEY MESSAGE 1: Strong to severe thunderstorms possible this evening and again late tonight.

The hot and humid conditions across the region will provide moderate instability across the region. SPC mesoanalysis indicates that SBCAPE may peak around 4000 J/kg with MLCAPE around 2500 J/kg. The 12Z KCHS sounding observed a freezing level around 15.5 kft. The thermo profiles along with effective bulk shear around 20 kts may support a few severe thunderstorms this afternoon and evening. Severe thunderstorms along the sea breeze may remain pulse-like where 55 dBZ cores that reach up to 29-30 kft. However, the increasing shear may support weakly organize multicell clusters across inland GA and SC. The primary thunderstorm hazards this afternoon and evening will be isolated damaging wind gusts and cloud-to-surface lightning. The most likely time window for severe thunderstorms is expected between 5-9 PM. Storm motions this afternoon and evening are forecast to remain around 15 mph.

Tonight, the center of low pressure associated with the remnants of Arthur will pass generally along and north of the I-20 corridor. High resolution guidance indicates that a band of thunderstorms associated with the system may sweep east to SE GA and SC after 3 AM tonight. Generally, this line should weaken as it push east, over a somewhat worked over air mass and increasing overnight stability. However, increasing shear may result in some organization of thunderstorm clusters, with the potential for severe wind gusts. This scenario appears most likely across SE GA and the southernmost SC counties during the pre-dawn hours Friday morning. The environment could support some rotating updrafts, leading to a non- zero risk for tornadoes, primarily across SE GA.

On Friday, the line of showers and thunderstorms should push offshore shortly after sunrise. A lingering trough may remain across SE GA through Friday afternoon. This feature may serve as a focus for afternoon to early evening thunderstorms. Otherwise, conditions will remain humid with temperatures peaking in the upper 80s.

KEY MESSAGE 2: A more typical summertime pattern is expected for the weekend into next week with daily shower and thunderstorm chances. Hot and humid conditions are expected Monday and Tuesday.

A front in the vicinity on Saturday will eventually wash out, with the region to become positioned between high pressure offshore and an approaching cold front Monday into Tuesday. Shower and thunderstorm chances will be in the forecast each day, with coverage peaking in the afternoon and evenings when instability is maximized. Organized severe weather potential is low, but cannot rule out a couple strong to severe storms each day during this time of year.

Also of note, hot and humid conditions are expected Monday and Tuesday ahead of an approaching cold front. Heat indices could reach the 105-110F range, particularly along the coastal counties. We will need to watch the potential for Heat Advisories.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

Prior to the 0Z TAFs, KCLX detected a cluster of thunderstorms approaching KSAV. The KSAV TAF will initialize with TS with a TEMPO until 3Z. The environment across KCHS and KJZI should be generally worked over and stabilized, some light rain is possible through 3Z. Overnight, the remnants of Arthur will track generally over the GA/SC I-20 corridor. A band of convection is expected to approach the terminals late tonight, timed between 10-14Z. This convection will be highlighted with TEMPO for -TSRA. A steepening pressure gradient should yield gusty west winds after sunrise, with gusts around 25 kts through Friday morning.

Extended Aviation Outlook: Brief periods of flight restrictions possible with any showers and thunderstorms.

MARINE

Through this evening, the pressure pattern will support southwest winds between 15 to 20 kts with gusts into the mid 20s. Wave heights are forecast to remain between 3 to 5 ft. Some thunderstorms could push off the SC coast this evening, possibly requiring Special Marine Warnings.

Tonight into Friday, the approach of the remnants of Arthur will increase the pressure gradient across the waters. Gale wind gusts appear likely over the SC nearshore and outer waters by late tonight and should remain into the early friday afternoon hours. Gale Warnings have been issued for the SC waters outside the CHS Harbor. Elsewhere, Small Craft Advisories will remain in effect.

Saturday through Tuesday: Marine conditions will subside Saturday with no additional concerns through the weekend. Another front could approach the area Monday into Tuesday, leading to increasing winds and seas. Gusts could approach 25 knots at times especially in the afternoons, but looks fairly marginal for Small Craft Advisories at this time.

Rip Currents: Increasing swells and gusty winds will lead to a Moderate risk for rip currents at South Carolina beaches Friday.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory from midnight tonight to 4 PM EDT Friday for AMZ340. Small Craft Advisory until 6 AM EDT Friday for AMZ360. Gale Warning from 6 AM to 4 PM EDT Friday for AMZ360-362-380- 382. Small Craft Advisory until 6 AM EDT Friday for AMZ362. Small Craft Advisory from 2 AM to 5 PM EDT Friday for AMZ364. Small Craft Advisory from 2 AM to 8 PM EDT Friday for AMZ384.