textproduct: Charleston

WHAT HAS CHANGED

Update to issue a Coastal Flood Advisory.

KEY MESSAGES

- 1) Excessive heat will remain a concern into next week.

- 2) Risk for Thunderstorms through Thursday.

DISCUSSION

KEY MESSAGE 1: Excessive heat will remain a concern into next week.

Thursday into Next Week: This aforementioned ridge will strengthen tomorrow (8/13) and Friday, yielding west- northwesterly flow across the region. This will yield afternoon highs from the mid to upper 90s (with some spots briefly hitting 100F). In addition to the extreme temperatures, it'll be quite humid outside with dewpoints in the mid to upper 70s. Expect PWAT values to range from 2.0 to 2.2 inches with the highest moisture generally located along and east of the I- 95 corridor. Afternoon heat index values west of I-95 will likely reach 105F to 108F with values reaching as high as 117F along and east of I-95. Therefore, a Extreme Heat Warning has been issued for the coastal counties from 11AM to 8PM tomorrow, and a Heat Advisory has been issued for the rest of the forecast area for the same timeframe. We will likely need heat headlines again for Friday (8/14).

As this prominent ridge continues to linger across the Southeast through the weekend and into early next week, expect similar conditions to Thursday and Friday with heat index values reaching upwards of 117F along the coastal corridor (along and east of I-95) and ranging from 105F to 112F west of I-95. This will likely necessitate additional heat headlines through early next week.

KEY MESSAGE 2: Risk for Thunderstorms through Thursday.

Thursday: A prominent ridge will continue to build across the Southeast tomorrow (6/13), with a well-defined shortwave reaching the forecast area by late afternoon into the early evening. Near- term guidance (HREF, HRRR, and NAM12) continues to indicate a solid band of thunderstorms developing across the Midlands and then tracking across southeast Georgia in the early to late evening. Some showers and thunderstorms could initiate in the afternoon (19-20Z) along the coastline as this shortwaves nears the region. The environment will feature moderate instability with SBCAPE values ranging from 2000 to 2500 J/kg with weak shear (50 to 100 m^2/m^2), yielding the possibility of a few strong to severe wind gusts within the stronger thunderstorms.

AVIATION /00Z THURSDAY THROUGH MONDAY/

VFR conditions are expected to prevail at KCHS, KJZI, and KSAV through 00z Friday. The main forecast challenge will be Thursday late afternoon or evening thunderstorm potential. Confidence isn't particularly high, and the best thunderstorm potential likely doesn't begin until very late in the 00z TAF period. Therefore, we have not introduced any mention of thunder at this time.

Extended Aviation Outlook: Periodic flight restrictions are expected in the afternoons with the chance of showers and thunderstorms through the weekend.

MARINE

Tonight: West to southwest winds will prevail through tonight. Winds will remain less than 15 kt with seas 3 ft or less.

Thursday through Sunday: Marine conditions will remain on the tranquil side as a weak coastal trough sets up across the Atlantic tomorrow (8/13) and persists through the weekend. Expect southwesterly winds to range from 10 to 15 kts with gusts up 20 kts possible through the period. Weak south-southwesterly swell will continue to taper into the waters through the weekend yielding 2 to 3 ft seas.

Coastal Flooding: The evening high tide at Charleston is coming up around 8:45 pm this evening. The current tide departure is running around 0.7 ft and we only need 0.45 ft to reach 7.0 ft MLLW. This tide departure will likely diminish through high tide but it looks more likely we will hit 7.0 ft MLLW. Therefore, a Coastal Flood Advisory has been issued for Charleston and coastal Colleton counties.

CLIMATE

Record High Temperatures:

August 13: KCHS: 100/1995 KCXM: 98/1913 KSAV: 98/2010

August 14: KCHS: 102/1995 KSAV: 102/1925

August 15: KCHS: 96/2023 KCXM: 99/1918 KSAV: 100/1918

August 17: KCHS: 102/1954 KSAV: 102/1954

August 18: KCXM: 97/1995 KSAV: 100/1995

Record High Minimum Temperatures:

August 13: KCHS: 81/2023

August 14: KCHS: 80/2023 KCXM: 83/2023 KSAV: 80/2023

August 15: KCHS: 78/1995 KCXM: 83/2021 KSAV: 80/1995

August 16: KCHS: 78/2019 KCXM: 83/2016 KSAV: 78/2019

August 17: KCHS: 80/2017 KCXM: 83/2017 KSAV: 78/2017

August 18: KCHS: 80/2017 KCXM: 82/2017 KSAV: 78/2010

CHS WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory from 11 AM to 8 PM EDT Thursday for GAZ087-088- 099>101-114-115-137-216-238. Extreme Heat Warning from 11 AM to 8 PM EDT Thursday for GAZ217>219-239>241. SC...Heat Advisory from 11 AM to 8 PM EDT Thursday for SCZ040- 042>045-147. Extreme Heat Warning from 11 AM to 8 PM EDT Thursday for SCZ148>152. Coastal Flood Advisory until 10 PM EDT this evening for SCZ149- 150. MARINE...None.