textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section has been updated for the 12Z TAF issuance.

KEY MESSAGES

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

- 2) There is a risk of strong thunderstorms today.

DISCUSSION

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

Today into Next Week: A large-scale ridge across much of the South Central United States will expand eastward today through late week, becoming centered across the Deep South and Southeast United States and favoring a warm west/northwesterly aloft. Ample sunshine will promote strong sfc heating during the next couple days, with 1000- 850 mb thickness levels supportive of afternoon highs in the mid- upper 90s, with some locations touching 100 degrees away from the coast through much of the weekend. In addition to hot temperatures, conditions will be quite humid with sfc dewpts in the mid-upper 70s each day. Although some mixing out of sfc dewpts is anticipated inland with the downslope wind setup locally, a sea breeze will eventually shift higher moisture content onshore each day for at least a few hours. This will likely result in the higher heat/moisture combination along coastal zones (along/east of I-95) for the next couple days, with heat index values up to the 110-115 range this afternoon and again Friday afternoon. Further inland, heat index values should top out in the 105-110 degree range. Given the setup and expected heat index values, an Extreme Heat Warning remains in effect for coastal counties from 11 AM to 8 PM today while remaining areas are included in a Heat Advisory for the same time period. The slightly more favorable position of the synoptic ridge supports slightly higher heat index values along the coastal corridor Friday. Therefore, an Extreme Heat Watch has been issued for all Southeast SC/GA coastal zones from 11 AM to 8 PM Friday afternoon. Another Heat Advisory could be needed for inland areas on Friday as well.

Hot/humid conditions likely remain across the Southeast United States late weekend into early next week with the large-scale ridge centered over or nearby, although a front could lead to greater shower/thunderstorm coverage that limits maximum heat conditions. Additional heat headlines could be needed through early next week.

KEY MESSAGE 2: There is a risk of strong thunderstorms today.

Strong ridging aloft will persist over the southeastern states today while a shortwave ripples across the northern periphery of the ridge. CAMs have struggled the last few days to get a handle on convection given the northwesterly flow at the surface, but the shortwave could be enough forcing to trigger thunderstorms across the SC Midlands. The latest runs of the HRRR and the 00Z HREF depict some convection firing in the later afternoon hours and tracking into the SC Lowcountry and Southeastern GA into the evening. Additionally, isolated convection is possible with the afternoon sea breeze. Unlike on Wednesday, the sea breeze shouldn't be pinned at the coast and looks to be progressive this afternoon. The forecast features slight chance thunderstorms this afternoon. Any storms that are able to form or track into the forecast area have the chance to become strong. The environment this afternoon is forecast to have DCAPE values upwards of 1000 J/kg. The main threat this afternoon would be damaging wind gusts with any of the stronger thunderstorms.

AVIATION /12Z THURSDAY THROUGH MONDAY/

VFR conditions are expected to prevail at CHS/JZI/SAV terminals through 12Z Friday. However, there is a low risk for an isolated shower and/or thunderstorm to impact the terminals this afternoon, perhaps near a mid-late afternoon sea breeze. Confidence remains too low to include mention of showers/thunderstorms and associated MVFR conditions with the 12Z TAF issuance.

Extended Aviation Outlook: Prevailing VFR.

MARINE

Today and Tonight: Conditions are expected to remain fairly quiet across local waters between the western periphery of an Atlantic high and weak troughing inland. Light westerly winds will turn southerly this afternoon, topping out near 10-15 kt along the coast where a sea breeze develops, then shifts inland mid-late day. There could be some modest nocturnal surging during evening hours with gusts up to 15-20 kt prior to midnight. Seas will be no larger than 2-3 ft.

Friday through Monday: Conditions are expected to remain below Small Craft Advisory criteria into the weekend and early next week. A weak coastal trough will persist across the marine waters this weekend and into the start of next week. This set up will keep conditions across the marine waters breezy with southwesterly winds gusting around 15 knots with occasional gusts to 20. 2 to 3 ft seas are expected across the marine zones this week.

Coastal Flooding: Tide levels could remain elevated due to the recent perigee and new moon during the evening high tide cycle, although a south-southwesterly wind should keep tidal departures less favorable for a coastal flood threat. Should onshore winds linger longer than anticipated, minor coastal flooding (~7.0 ft MLLW) could become an issue in the Charleston Harbor during the high tide this evening, which occurs ~9:30 PM.

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 this morning to 8 PM EDT this evening for GAZ087-088-099>101-114-115-137-216-238. Extreme Heat Warning from 11 AM this morning to 8 PM EDT this evening for GAZ217>219-239>241. Extreme Heat Watch from Friday morning through Friday evening for GAZ217>219-239>241. SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ040-042>045-147. Extreme Heat Warning from 11 AM this morning to 8 PM EDT this evening for SCZ148>152. Extreme Heat Watch from Friday morning through Friday evening for SCZ148>152. MARINE...None.