textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section was updated for the 12Z.

KEY MESSAGES

- 1) Scattered to numerous thunderstorms expected each afternoon and evening through this weekend. Isolated excessive rainfall possible this afternoon along the Interstate 95 corridor.

DISCUSSION

KEY MESSAGE 1: Scattered to numerous thunderstorms expected each afternoon and evening through this weekend. Isolated excessive rainfall possible this afternoon along the Interstate 95 corridor.

Satellite water vapor showed a mid-level longwave trough extending from eastern Canada south to the Gulf. East of the trough, a band of deep moisture covered a large area from the Gulf across the Southeast U.S. Near term guidance indicates a few vort maxes within the moisture plume, with the consensus of the guidance indicating that one or two disturbances tracking over SE GA this afternoon. The approach and passage of these mid-level features concurrent with the sea breeze should focus the development of convection. Forecast soundings indicate PW values around 2.25 inches with warm cloud depth in excess of 12 kft. In addition, SBCAPE should peak around 1500 J/kg with LFC generally below 3 kft. Showers and thunderstorms should readily develop along and ahead of the sea breeze and mid- level disturbances. The forecast will feature PoPs as high as 90% across the I-95 corridor of GA/SC. Given the high coverage of convection, storm motions around 15 mph, and the deep tropical moisture, heavy to excessive rainfall is the primary hazard today. 0Z HREF indicates a large area under 70% for 1"/3hr and 30% for 3"/hr along the I-95 corridor. Based on the timing of the sea breeze, the heavy rainfall could potentially concentrate in an area between Savannah to Springfield to Ridgeland. After collaboration with WPC, a Slight Risk for excessive rainfall was posted for the SC Lowcountry and most of SE GA. Flood Advisories or Flash Flood Warnings could be needed this afternoon into early this evening. Fortunately, forecast soundings indicate that DCAPE values may remain limited to 800 J/kg or less with freezing levels as high as 15 kft, keeping the risk of severe thunderstorms low.

Weak shortwaves aloft may continue some isolated-scattered showers and thunderstorms Saturday morning, though we'll have to see where the aforementioned front ends up to see how long that may linger. While there will likely be a break from the rain during the mid- morning to early afternoon hours, additional showers and thunderstorms are expected as the anticipated afternoon sea-breeze pushes ashore. While 1500-2000 J/kg of SBCAPE are anticipated, the lack of flow aloft should keep thunderstorms from getting well organized, thus keeping the risk for strong to severe thunderstorms on the low end. However, given the slow storm motions and precipitable water values in excess of 2 inches, locally heavy rainfall cannot be ruled out. HREF has scattered 50-70% chances for an inch along and west of I-95, decreasing into the 20-30% probability range for 3 inches. Given the higher amounts of cloud coverage and chances for rain, high temperatures on Saturday look to be in the lower to upper 80s across the region.

Expect lighter and less focused rainfall for Sunday and Monday as weak ridging occurs aloft, with another weak front beginning to move towards the area from the west. Weak mid-level warm air advection will bring additional chances for scattered showers and thunderstorms throughout the period, though the best chances will occur during the afternoon hours as the expected sea-breeze pushes ashore. High temperatures on both days will be near-normal, in the mid 80s to lower 90s on Sunday, marginally warmer on Monday in the upper 80s to mid 90s on Monday.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

12Z TAFs: Satellite water vapor showed a mid-level longwave trough extending from eastern Canada south to the Gulf. East of the trough, a band of deep moisture covered a large area from the Gulf across the Southeast U.S. Near term guidance indicates a few vort maxes within the moisture plume, with the consensus of the guidance indicating that one or two disturbances tracking over SE GA this afternoon. The approach and passage of these mid-level features concurrent with the sea breeze should focus the development of convection. Each TAF will feature a mention of VCSH around 17-18Z with TEMPOs for TSRA from 18-23Z. KSAV appears to be a greatest risk for TSRA this afternoon and evening. Otherwise, TAFs will indicate light west winds before the sea breeze, shifting from the SSW following the sea breeze.

Extended Aviation Outlook: Showers and thunderstorms will bring brief flight restrictions through the weekend, especially during the afternoons.

MARINE

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

Extended Marine: No large-scale marine concerns, with daily chances for showers and thunderstorms. Weak winds Saturday morning will turn east-southeasterly by the late afternoon hours, continuing through Sunday. Winds remain weak to start off the work-week.

CHS WATCHES/WARNINGS/ADVISORIES

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