textproduct: Charleston

WHAT HAS CHANGED

Discussion and Marine sections updated to reflect latest forecast thoughts.

KEY MESSAGES

- 1) Heat will remain a concern into the middle of next week.

- 2) Strong to severe thunderstorms are possible each afternoon through the weekend.

DISCUSSION

KEY MESSAGE 1: Heat will remain a concern into the middle of next week.

Rest of Today through Sunday: Our annual relocation to the face of the sun continues as planned as heat indices today have climbed back into the 108 to 112 range this afternoon. Expect this heat to continue right into the weekend with the rather impressive upper ridge firmly locked in place over the southeast. With plenty of sun to go around and overall profiles supportive of temperatures in the mid to upper 90s and a few locations touching triple digits away from the coast, expect no respite from the heat in the near future. In addition to hot temperatures, conditions will remain humid with sfc dewpts in the mid-upper 70s each day and even some rather impressive 80s dewpoints behind a slowly advancing seabreeze each day. A west- northwest downsloping wind should result in a slightly delayed seabreeze the next few afternoons, promoting some mixing out of sfc dewpts inland, but moisture pooling along/near the sea breeze will eventually shift higher moisture content onshore each day for at least a few hours as well. Overall 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 late morning into the afternoon and again on Saturday.The only fly in the ointment looks to be the coverage of showers and thunderstorms along the slowly advancing seabreeze during the late afternoon. This looks to be especially true for areas around the Charleston metro/tri-county area where coverage looks to peak during the late afternoon. This could keep things a bit cooler than the past few days; however, cooler is used likely as thats like saying a ghost chili is cooler than a carolina reaper pepper. Despite the uncertainty in convection we went ahead and upgraded areas along the coast to an Extreme heat warning with a heat advisory for areas further inland. By Sunday the ridge should begin to strengthen once again leading to maybe a few degrees warmer across the board Expect products to continue into Sunday.

Early to Middle of Next Week: The upper ridge should re-strengthen across the deep south by next week. Hot/humid conditions will likely remain across the Southeast United States. The ridge looks to be the strongest on Monday through Wednesday as heat indices likely climb well into heat advisory range and possibly another round of extreme heat watches and warnings for coastal areas. This is reflected in some of the longer range ensemble guidance with ECMWF EFI MAX T climbing into the 80 to 90th percentile meaning increasingly likely for a more significant heat with respect to area climatology. By the middle part of the the week, The only limiting factor at this time looks to be increased coverage of showers and thunderstorms Tuesday and Wednesday as some increased flow tries to work its way into the area. Record warmth is possible next week with guidance suggesting several areas of 100+ temps Monday/Tuesday and little to no shower/thunderstorm activity. After Wednesday, the upper ridge should begin to shift eastward and breakdown bringing a break from the heat wave.

KEY MESSAGE 2: Strong to severe thunderstorms are possible each afternoon through the weekend.

With the combination of heat and humidity (mentioned in Key Message 1) and our area being on the eastern periphery of the upper ridge, afternoon showers and thunderstorms will be possible each afternoon. Depending on the model, SBCAPE values peak in the 2,000-2,500 J/kg range, with DCAPE values upwards of 800 J/kg to 1000 J/kg. The general consensus is that there should be isolated to scattered convection each afternoon through the weekend. These details will need to be refined with each forecast. But the storms are most likely to start along the sea breeze and then shift inland, with outflow and boundary interactions playing a role in storm formation and persistence. Given the aforementioned instability, strong to severe thunderstorms are possible. The main threat would be damaging winds. But heavy rainfall is also a concern due to weak steering flow. Backbuilding and/or training of storms could drop enough rainfall to generate very localized flooding.

AVIATION /19Z FRIDAY THROUGH WEDNESDAY/

VFR conditions prevail at CHS/JZI/SAV terminals this afternoon. Convective coverage this afternoon will be limited, but scattered storms mainly along the GA coast could bring temporary restrictions, especially at SAV, mid-to-late afternoon. Otherwise, a moderate sea breeze will push inland this afternoon, dissipating overnight as light and variable winds prevail.

Extended Aviation Outlook: Afternoon showers and thunderstorms will bring brief flight restrictions through the weekend.

MARINE

Tonight and Sunday: Conditions are expected to remain quiet across local waters between the western periphery of an Atlantic high and weak troughing inland, although thunderstorms that develop over land could shift offshore late afternoon into early evening hours. A few thunderstorms could remain strong when shifting across coastal areas. Outside thunderstorms, southwesterly winds around 10 kt this morning should turn more southerly and gust up to 15-20 kt this afternoon, then persist into evening hours, before slowly weakening and returning to a southwesterly direction overnight. Seas should be no larger than 2-3 ft.

Extended Marine: There will be areas of High pressure in the western Atlantic and the northern Gulf, while surface troughing will be over the Southeast U.S. The interaction between all of these synoptic features will generate a typical summertime wind pattern. Winds will generally be from the SW, backing a bit each day and veering some each night. The strongest winds should be during the day, especially closer to the coast due to the sea breeze. Seas will mainly be in the 2-3 ft range.

CLIMATE

Record High Temperatures:

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

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

August 16: KCHS: 99/1954 KSAV: 100/1954

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

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

Record High Minimum Temperatures:

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 until 8 PM EDT this evening for GAZ087-088- 099>101-114-115-137. Heat Advisory from 11 AM to 8 PM EDT Saturday for GAZ087-088- 099>101-114-115-137. Extreme Heat Warning until 8 PM EDT this evening for GAZ216>219-238>241. Extreme Heat Warning from 11 AM to 8 PM EDT Saturday for GAZ216>219-238>241. SC...Heat Advisory until 8 PM EDT this evening for SCZ040-042>044. Heat Advisory from 11 AM to 8 PM EDT Saturday for SCZ040- 042>044. Extreme Heat Warning until 8 PM EDT this evening for SCZ045- 147>152. Extreme Heat Warning from 11 AM to 8 PM EDT Saturday for SCZ045-147>152. MARINE...None.