textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section has been updated for the 18Z TAF issuance.

KEY MESSAGES

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

- 2) A few isolated strong to severe thunderstorms are possible this afternoon.

DISCUSSION

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

Rest of Today: As amplified ridging remains in place across the Deep South and the Southeastern CONUS, afternoon temperatures will reach into mid to upper 90s with low 90s along the coastline. These temperatures combined with dewpoints in the mid to upper 70s (highest across the coastal counties) yield heat index values in the 105 to 112 range. Thus, a Heat Advisory shall remain across the Lowcountry and southeast Georgia through 8PM EDT this evening. Some afternoon showers and thunderstorms could provide some relief from the heat and possibly short the duration of the Heat Advisory across portions of the area late this afternoon.

Monday and Tuesday: Expect hot and humid conditions to continue across the region as large-scale ridging remains in position across the Deep South. These look to be the hottest days of the week with temperatures reaching mid to upper 90s (with some spots peaking around 100-101F). Mixed in CONSShort and NBM for the dewpoints as this setup favors strong mixing across the inland areas and portions east of I-95 as the seabreeze remains somewhat pinned near the coastline in the early afternoon. This will lead to some uncertainty with the maximum heat index values and duration of peak heating hours Monday and Tuesday. An Extreme Heat Warning has been issued for the coastal counties (including inland Berkeley) with a Heat Advisory across the remaining inland counties on Monday from 11Am to 8PM EDT. We will likely need additional heat headlines on Tuesday as well.

Wednesday and Thursday: This aforementioned ridge will start to weaken by the mid-week and summertime afternoon convection should make a reappearance. This pattern will likely still favor Heat Advisory conditions prior to shower and thunderstorm development (esp. across the coastal counties) on Wednesday and Thursday.

KEY MESSAGE 2: A few isolated strong to severe thunderstorms are possible this afternoon.

The heat and humidity discussed in Key Message 1 will also result in moderate instability (SBCAPE 2500-3000+ J/kg) building across the region this afternoon. However, with the subsidence from the upper level ridge, and the lack of flow aloft leading to rather low 0-6km shear, pulse showers and thunderstorms rather than organized convection are expected. Will likely need to wait on the expected afternoon sea-breeze to get the initial round going, with additional development possible on outflow and boundary interactions. Given the very warm environment and expected pulse-like nature, hail seems unlikely. However, with DCAPE values of 700-1000 J/kg and decent low- level lapse rates of 7-8 deg C/km, a few isolated strong to severe thunderstorm gusts cannot be ruled out. The 12Z CHS sounding revealed a PWAT of 2.5 inches, which looks to be a new daily max, and with 2.2-2.5" PWATs spread over the rest of the region locally heavy rainfall may also occur given the weak steering flow. Chances for showers and thunderstorms wane into the evening hours.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

16/18Z TAFs: Showers and thunderstorms have begun initiating near KSAV. Thus, a TEMPO was added at KSAV for 18-19Z. A PROB30 group has been maintained at KCHS/KJZI/KSAV terminals from 20-24Z for thunderstorms and MVFR conditions. By 02Z, VFR conditions should return and persist through 18Z Monday.

Extended Aviation Outlook: Periodic flight restrictions are expected due to afternoon showers and thunderstorms Tuesday through Thursday.

MARINE

Rest of today into tonight: 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 this afternoon could shift offshore into the early evening hours and produce gusty winds. Outside of thunderstorm activity, southerly winds with gust up to 10-15 kt this afternoon and persisting into the evening, before slowly weakening and returning to west/southwest 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 persist 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 16: KCXM: 97/1954 KSAV: 100/1954

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

August 18: KCHS: 101/1995 KCXM: 97/1995 KSAV: 100/1995

August 19: KCHS: 98/1983 KCXM: 98/1895 KSAV: 99/1900

August 20: KCHS: 97/2005

Record High Minimum Temperatures:

August 16: KCHS: 78/2019 KSAV: 78/2019

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

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

August 19: KCHS: 79/2010 KCXM: 83/2021 KSAV: 79/1878

August 20: KCHS: 78/2017 KCXM: 82/2017

August 21: KCHS: 79/2010 KCXM: 82/2023 KSAV: 80/1902

August 22: KCHS: 79/2023

CHS WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory until 8 PM EDT this evening for GAZ087-088- 099>101-114-115-137-216>219-238>241. Heat Advisory from 11 AM to 8 PM EDT Monday for GAZ087-088- 099>101-114-115-137-216-218-238. Extreme Heat Warning from 11 AM to 8 PM EDT Monday for GAZ217- 219-239>241. SC...Heat Advisory until 8 PM EDT this evening for SCZ040-042>045- 147>152. Heat Advisory from 11 AM to 8 PM EDT Monday for SCZ040-042>044- 147. Extreme Heat Warning from 11 AM to 8 PM EDT Monday for SCZ045- 148>152. MARINE...None.