textproduct: Charleston

WHAT HAS CHANGED

Updated the Aviation section to reflect the 00z TAFs.

KEY MESSAGES

- 1) There is risk for locally heavy rainfall and isolated flash flooding across Southeast Georgia into the western South Carolina Lowcountry this afternoon and evening. A few strong to marginally severe thunderstorms are possible.

- 2) Scattered to numerous showers and thunderstorms will bring the potential for heavy rainfall, localized flooding, and/or gusty winds Sunday through early next week.

DISCUSSION

KEY MESSAGE 1: There is risk for locally heavy rainfall and isolated flash flooding across Southeast Georgia into the western South Carolina Lowcountry this afternoon and evening. A few strong to marginally severe thunderstorms are possible.

This afternoon, regional radar composite indicated a developing band of thunderstorms across southern GA, tracking northward. These storms will likely continue northward across the forecast area, partially supported by MLCAPE between 2500-3000 J/kg. Also, with the arrival of the thunderstorms, PW values will build to 2 to 2.2". These storms and associates cold pool may interact with the sea breeze to produce numerous to widespread showers and thunderstorms during the late afternoon and evening hours. High resolution guidance indicates that multiple cell mergers or training storms may occur, especially in the vicinity of the cold pool and sea breeze. These processes could result in local areas of 2 to 4 inches of rain this afternoon and evening. The area of heaviest rainfall potential was highlighted well with the 12Z HREF, indicating a 50% of 3"/3hr along and west of I-95 across SE GA/SC. Thunderstorms should gradually dissipate during the mid to late afternoon. However, the approach of a longwave H5 trough may trigger additional showers and thunderstorms along the coast.

KEY MESSAGE 2: Scattered to numerous showers and thunderstorms will bring the potential for heavy rainfall, localized flooding, and/or gusty winds Sunday through early next week.

Sunday: As the aforementioned system continues to trek eastwards, the region remain in the warm sector of the surface low pressure moving across the Ohio River Valley, with mid-level troughing expected to continue throughout the day. PWATs are expected to remain high between 2.2 - 2.4 inches (above the 90th percentile of climatology), and when combined with the warm air advection aloft and scattered shortwaves, scattered to numerous showers and thunderstorms are expected throughout the day. CAPE profiles remain long and skinny through the day, which indicates potential for heavy rainfall. HREF has scattered 70% chances for an inch in 3 hours with very isolated 10% chances for 3 inches, while the REFS has lesser chances for an inch (40-50%) though still isolated 10% chances for 3 inches. As for the severe potential, with 1500-2000 J/kg of ML CAPE, highest in the late morning to mid afternoon hours, there remains potential for isolated strong to severe thunderstorms. Given the potential for heavy downpours amidst a DCAPE environment of 500-1000 J/kg, strong wind gusts remain the primary risk. The risks for both heavy rainfall and severe potential are highest for our inland areas, lowest for areas along the coast.

Monday: The aforementioned surface low pressure moves northeast into the Quebec province, with the trailing cold front extending down into Georgia and southern Alabama. Aloft, the trough turns into a closed upper level low, with scattered shortwaves continuing to overspread the region from south to north. PWATs decrease into the 2.0-2.2" range, and instability wanes to near 1000 J/kg, decreasing both the heavy rainfall and severe weather risks. However, given the expected preceding rainfall, the chances for locally heavy rainfall will persist especially for areas that saw recent heavy rains.

Tuesday into the middle of the week: Previously, models brought the cold front through the region bringing an end to the wet conditions, though the latest 12Z guidance now has the front stalling off to our west as a surface high pressure builds and moves in from the Atlantic.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

00Z TAFs: Mostly VFR conditions will prevail this evening with mostly light rain falling mainly west of I-95. Rain across the area should diminish over the next hour or two with no impacts to area terminals expected. MVFR ceilings will likely move in after 06Z tonight with possibly some IFR ceilings south of the Georgia line impacting SAV around 09Z to 13z. Scattered showers and possibly an isolated thunderstorm will likely develop along the coastline resulting in possible reductions at CHS, JZI and SAV around 07Z to 12z. VFR conditions will return by 15Z to 18Z; however, increased coverage of thunderstorms will result in continued temporary reductions from 18z to 21z at all area terminals. Winds will remain out of the south-southwest around 10 knots throughout the daytime tomorrow.

Extended Aviation Outlook: Periodic flight restrictions are expected in showers and thunderstorms through early next week. Locally heavy rainfall may produce brief IFR or lower visibility restrictions.

MARINE

This afternoon: The National Weather Service Doppler Radar and satellite images indicated a boundary with isolated showers near the entrance of the Charleston Harbor. This line was associated with a observed waterspout on Folly Beach at 233 PM. This boundary should continue to drift north through 430 PM. The environment may support the formation of additional waterspouts along the boundary this afternoon.

Tonight, the pattern will support southwest winds between 15 to 20 kts. Wave heights are forecast to build to 2 to 4 ft by late tonight.

Sunday through Thursday: The pressure gradient will strengthen Sunday as broad low pressure develops inland with an approaching front and high pressure remaining in the Atlantic. Southwesterly winds will increase during the afternoon, with frequent gusts between 25 and 30 kt expected across the local waters. In addition, wave heights are forecast to increase to 4 to 7 feet Sunday evening. Small Craft Advisories have been issued for the nearshore marine zones out to 20 nm and the outer Georgia waters from 20-60 nm, as well as the Charleston Harbor. Conditions should gradually improve Monday night, with benign wind and sea conditions expected for Tuesday through the rest of the period.

Rip Currents: Gusty southwest winds combined with a 6 to 7 second swell and wave heights of 4-5 feet will support an elevated rip current risk on Sunday. A Moderate Risk of Rip Currents has been expanded to include the southeast Georgia beaches, remaining across the southeast South Carolina beaches. For Monday, Moderate Risk of Rip Currents continue for areas from coastal Colleton county down to the Altamaha River, with a High Risk of Rip Currents risk for the Charleston county coastline as strongest winds occur along the Charleston county coast.

CLIMATE

Record High Minimum Temperatures:

August 1: KCHS: 81/1999 KCXM: 86/1999 KSAV: 79/2020

August 2: KCHS: 79/2022 KCXM: 84/1999 KSAV: 80/1886

August 5: KCHS: 79/1980 KCXM: 82/1991 KSAV: 80/1883

August 6: KCHS: 79/1991 KCXM: 82/2006 KSAV: 80/1899

August 7: KCHS: 79/2007 KCXM: 83/2007 KSAV: 80/1879

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory from noon Sunday to 2 AM EDT Monday for AMZ340. Small Craft Advisory from noon Sunday to 2 AM EDT Tuesday for AMZ360-362. Small Craft Advisory from noon Sunday to 8 AM EDT Monday for AMZ364. Small Craft Advisory from noon Sunday to noon EDT Monday for AMZ384.