textproduct: Charleston

WHAT HAS CHANGED

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

KEY MESSAGES

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

- 2) Strong to severe thunderstorms are possible this afternoon.

DISCUSSION

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

Today: A warm pattern will remain in place with large-scale ridging across the Deep South and Southeast United States. Much like the previous couple days, strong heating this morning into early afternoon should support high temps in the mid 90s away from the immediate beaches. These temps along with sfc dewpts in the mid- upper 70s (highest across coastal counties where impacts of mixing out of low-lvl moisture is less likely) support heat index values in the 106-111 range and the continuation of a Heat Advisory across Southeast South Carolina and Southeast Georgia from 11 AM to 8 PM. However, convective coverage should become a larger influence today with scattered showers/thunderstorms developing during peak heating hours. This could provide some relief from the heat this afternoon, and possibly shorten the duration of the Heat Advisory across some areas late day.

Monday and Tuesday: Hot/humid conditions will remain across the Southeast United States through the middle of the week with large- scale ridging centered across the Deep South and northern Gulf regions. Record warmth is possible, especially as the heat wave peaks with a downslope wind across the local area Monday and Tuesday. Some areas could see temps peak around 100 degrees each afternoon with little to no shower/thunderstorm activity. The setup favors strong mixing out of sfc dewpts across inland areas, and possibly east of I-95 should a sea breeze remain somewhat pinned near the coast into early afternoon, leading to some questions to maximum heat index values and duration during peak heating hours both days. The combination of hot temperatures and sfc dewpts in the low 70s inland and mid-upper 70s near the coast look to favor at least Heat Advisory level conditions early week, and the possibility of Extreme Heat Warning criteria across coastal counties.

Wednesday and Thursday: There are signs of the expansive ridge starting to weaken while scattered convection returns during peak heating hours. We should see another day of Heat Advisory conditions prior to showers/thunderstorms developing, especially along the coastal corridor. Thursday remains hot, but with a similar trend in the mid-upper pattern, although some hints of weak shortwave energy rounding the northeast periphery of the ridge could deliver greater cloud coverage and/or shower/thunderstorm activity to the region. Additional heat headlines could be needed.

KEY MESSAGE 2: Strong to severe thunderstorms are possible this afternoon.

The heat and humidity (mentioned in Key Message 1) will provide a moderate amount of instability across our area this afternoon. Models generally have SBCAPE values in the 2,000-2,500 J/kg range across our area with locally higher peaks. Likewise, DCAPE values should exceed 1,000 J/kg in some areas. There continues to be some minor differences between the various CAMS and the deterministic models. But when all of that is factored in, the general consensus is that there should be isolated to scattered convection forming along the sea breeze early this afternoon, and then shifting inland. The outflow and boundary interactions should again play a major role in storm formation and persistence. Given the aforementioned instability and DCAPE, strong to severe thunderstorms are possible across our entire area, with perhaps slightly higher potential south of I-16. The main threat is damaging winds. Though, heavy rainfall is also a concern due to the very weak steering flow. Backbuilding and/or training of storms could drop enough rainfall to generate very localized flooding with or maybe even flash flooding. The convection may start to shift back towards the coast late in the afternoon and early evening, but will then dissipate as the energy diminishes with sunset.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

VFR conditions are expected at CHS/JZI/SAV terminals through about 18Z today. The risk for isolated to scattered showers and/or thunderstorms increases during afternoon hours, and possibly lingers into evening hours. PROB30 groups remain at CHS/JZI/SAV terminals from 20-24Z today for thunderstorms (some possibly strong with gusty winds) and MVFR conditions. VFR conditions should then return by 02Z Monday and persist through 12Z Monday.

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

MARINE

Today and 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 could shift offshore late afternoon into early evening hours and produce gusty winds. Outside thunderstorms, light west/southwest winds around 5 kt this morning should turn more southerly and gust up to 10-15 kt this afternoon, then persist into evening hours, 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: KCHS: 99/1954 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 KSAV: 99/1900

August 20: KCHS: 97/2005 KSAV: 102/1900

Record High Minimum Temperatures:

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

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

August 20: KCHS: 78/2017 KCXM: 82/2017 KSAV: 82/1878

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>219-238>241. SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ040-042>045-147>152. MARINE...None.