textproduct: Charleston

WHAT HAS CHANGED

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

KEY MESSAGES

- 1) Heat will remain a concern into late week.

- 2) Afternoon and evening thunderstorm coverage will remain isolated through Thursday. An increase in thunderstorm coverage is expected Friday through the weekend.

DISCUSSION

KEY MESSAGE 1: Heat will remain a concern into late week.

Today: A warm pattern remains in place with large-scale ridging extending across much of the Deep South and Southeast United States. However, we should see the first signs of ridge weakening as a large- scale trough becomes positioned across the Great Lakes region. A west flow will limit overall convective coverage during peak heating hours and areas well inland are expected to see sfc dewpts mix out substantially, into the upper 60s west of I-95, therefore limiting the overall maximum heat index potential. However, coastal zones and across parts of Berkeley County should see sfc dewpts remain in the mid-upper 70s, especially with moisture pooling and/or an onshore wind associated with a sea breeze circulation. These zones are expected to experience the highest heat/humidity combination as sfc temps warm into the mid-upper 90s, prompting a Heat Advisory from 11 AM to 8 PM today. Record temps are also possible (see Climate Section below).

Thursday and Friday: The expansive ridge that has persisted across the region for the last week is expected to weaken late week with the approach of a large-scale trough this weekend. Until the anticipated change, we could see Heat Advisory conditions prior to scattered showers/thunderstorms developing Thursday afternoon, especially along the coastal corridor where afternoon highs reach the upper 90s and sfc dewpts remain in the mid-upper 70s. Locations inland should experience another day of strong mixing out of sfc dewpts into the upper 60s west of I-95. Friday remains warm as well, but convective coverage could become more substantial as shortwave energy associated with a large-scale trough approaches the Mid- Atlantic and Southeast states this weekend. Trends suggest afternoon highs to remain a few degrees "cooler" than the previous day given increasing chances of precipitation, limiting Heat Advisory potential across inland areas. However, should convective activity remain less than expected and/or delayed until late day, there remains a risk for Heat Advisory conditions across the coastal corridor on Friday.

KEY MESSAGE 2: Afternoon and evening thunderstorm coverage will remain isolated through Thursday. An increase in thunderstorm coverage is expected Friday through the weekend.

Today and Thursday: The above normal temperatures and stifling humidity will continue to generate instability this afternoon and again Thursday afternoon. However, models indicate convective coverage should remain isolated both afternoons. Any convection is most likely to form along the sea breeze and then shift inland, driven by outflow and boundary interactions. Strong to severe thunderstorms are possible each afternoon with the main threat being damaging winds. Heavy rainfall is also a concern due to the very weak steering winds and elevated PWATs. Any convection will decrease both evenings.

Friday into the Weekend: The pattern turns more active as a slow moving front approaches our area from the west and northwest. This should generate scattered to widespread thunderstorms starting Friday afternoon, continuing each afternoon through the weekend.

Even though the heat won't be as extreme Friday into the weekend, temperatures will remain above normal. SBCAPE values could still get quite elevated, along with DCAPE values. Strong to severe thunderstorms are possible each afternoon with the main threat being damaging winds. Heavy rainfall will also be a bigger concern due to the very weak steering winds and elevated PWATs. Flash flooding is possible and this has been highlighted in WPC's ERO.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

VFR conditions are expected at CHS/JZI/SAV terminals through 12Z Thursday. However, an isolated shower or thunderstorm can not be ruled out at the CHS terminal late day. There are also some signs of reduced vsbys at CHS/JZI late in the TAF period. Confidence remains too low to include MVFR conditions in the latest TAF issuance.

Extended Aviation Outlook: VFR through Thursday. Afternoon showers and thunderstorms could bring brief flight restrictions starting Friday.

MARINE

Today and Tonight: Conditions are expected to remain quiet across local waters between high pressure across the western Atlantic/Gulf and weak troughing inland. West winds 5-10 kt this morning should turn south with gusts up to around 15 kt this afternoon, strongest near the coast where a sea breeze develops. Winds should then return to southwest and weaken to 5-10 kt during the overnight period. Seas should be no larger than 2-3 ft.

Extended Marine: A typical summertime wind pattern is expected with winds/seas that are below Small Craft Advisory levels. Each day there will be some backing of the winds. They'll be the strongest along the land/sea interface due to the sea breeze. Each night winds will veer a bit. Seas will mainly be in the 2-3 ft range.

CLIMATE

Record High Temperatures:

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

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

August 21: KCHS: 100/1983 KSAV: 101/1902

Record High Minimum Temperatures:

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 KCXM: 82/2014 KSAV: 79/1902

August 23: KCXM: 81/2019 KSAV: 78/2016

CHS WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for GAZ217>219-239>241. SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ045-148>152. MARINE...None.