textproduct: Charleston

WHAT HAS CHANGED

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

KEY MESSAGES

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

- 2) A few strong to severe thunderstorms are possible each afternoon through Thursday. Scattered to widespread thunderstorms are expected Friday into the weekend.

DISCUSSION

KEY MESSAGE 1: Heat will remain a concern today into late 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 day, strong heating is expected during morning and afternoon hours with little to no relief from the heat in regards to shower/thunderstorm activity. Record warmth is possible as the intensity of the heat wave peaks with another day of favorable downslope flow across the local area. Many areas will see temps peak in the upper 90s to around 100 degrees, warmest along and east of the I-95 corridor, but away from the beaches. Despite some mixing out of low-lvl moisture across the local area late morning and afternoon, sfc dewpts in the mid-upper 70s support heat index values up to the 106-112 range inland to 113-119 range across the coastal corridor. An Extreme Heat Warning remains in effect from 11 AM to 8 PM today for SC/GA coastal counties and also includes Dorchester County, SC and Effingham County, GA. A Heat Advisory remains in effect from 11 AM to 8 PM today for all remaining inland areas as well.

Wednesday into Friday: There are signs of the expansive ridge starting to weaken while isolated to scattered convection returns during peak heating hours mid to late week. We could see Heat Advisory conditions prior to showers/thunderstorms developing Wednesday and Thursday afternoons, especially along the coastal corridor where maximum heating and sfc dewpts remain in the mid- upper 70s. Despite hot temperatures that peak in the upper 90s to perhaps 100 degrees in some spots Wednesday and Thursday, inland areas (west of I-95) should experience more substantial mixing out of sfc dewpts into the 60s. Friday remains warm (mid-upper 90s for most areas), but guidance supports greater convective coverage and some relief from the heat during peak heating hours, as shortwave energy associated with a large-scale trough approaches the Mid- Atlantic and Southeast states this weekend. Nevertheless, there remains a risk for heat headlines into Friday should convective coverage remain less or become more delayed.

KEY MESSAGE 2: A few strong to severe thunderstorms are possible each afternoon through Thursday. Scattered to widespread thunderstorms are expected Friday into the weekend.

The above normal temperatures and stifling humidity that have been persisting across our area for more than a week will continue to generate instability each afternoon this week. The various models continue to have differences regarding how much instability will be in place and where the highest values will be. Though, the ongoing trend has been a general consensus of SBCAPE values in the 2,000- 3,000 J/kg range with locally higher peaks each day. Likewise, DCAPE values should easily exceed 1,000 J/kg. There are larger differences with the latest CAMS and the deterministic models. The deterministic models generally have it dry this afternoon, along with Wednesday and Thursday afternoons. Meanwhile, the CAMs lean towards some convection this afternoon and Wednesday afternoon. Given the amount of instability in place, it's hard to say it'll be completely dry. It won't take much for at least isolated convection to form along the sea breeze this afternoon and then shift inland, and for the same thing to happen again Wednesday and Thursday afternoons. Any convection that manages to form should generate outflow, and that along with boundary interactions should play a major role in additional storm formation and persistence. 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 should dissipate each evening with the setting sun.

The pattern turns more active towards the end of the week, especially 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. But the fine details and largest threats will need to be better refined with future forecasts.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

VFR conditions are expected at CHS/JZI/SAV terminals through 12Z Wednesday. However, an isolated shower or thunderstorm can not be ruled out at the SAV terminal late day. A PROB30 group remains at SAV between 21-24Z today for thunderstorms and associated MVFR conditions.

Extended Aviation Outlook: Mainly 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 around 10 kt or less this morning should turn south with gusts up to 15-20 kt this afternoon, strongest near the coast where a sea breeze develops. Winds should then return to southwest and weaken to below 10-15 kt during the overnight period. 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 persists over the Southeast United States. The interaction between these synoptic features will support a typical summertime wind pattern with winds/seas that remain below Small Craft Advisory levels. In general, southwest winds should back to a more south direction each day, peaking in speed along the coast due to a sea breeze, then return to southwest during the overnight period. Seas will mainly be in the 2-3 ft range.

CLIMATE

Record High Temperatures:

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 KSAV: 102/1900

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

Record High Minimum Temperatures:

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 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 GAZ087-088-099-100-114-115-137. Extreme Heat Warning from 11 AM this morning to 8 PM EDT this evening for GAZ101-216>219-238>241. SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ040-042-043. Extreme Heat Warning from 11 AM this morning to 8 PM EDT this evening for SCZ044-045-147>152. MARINE...None.