textproduct: Charleston

WHAT HAS CHANGED

Aviation section updated to represent the 12Z TAF.

KEY MESSAGES

- 1) Heat remains a concern into Friday.

- 2) Increased risk for showers and thunderstorms into the weekend.

DISCUSSION

KEY MESSAGE 1: Hot and humid conditions will persist today.

Today should be the final day in this extended stretch of dangerous heat. High temperatures will peak back up in the mid to upper 90s, with heat indices of 105-110F. The highest heat indices will occur closest to the coast where a Heat Advisory has been issued. There will be convection developing in the afternoon, however it looks to be late enough where these areas look to reach 108+ for at least a couple of hours. No additional heat headlines are expected over the weekend as a mid level trough and associated surface front shifts into the region. Heat indices should generally remain below 105.

KEY MESSAGE 2: Increased risk for showers and thunderstorms into the weekend.

Friday: A more appreciable change in the pattern is expected on Friday as this mid-lvl ridge finally breaks down and broad troughing begins to build across the eastern half of the CONUS. Several embedded shortwaves are forecast to round the base of this trough while a slow-moving surface front approaches the region from the west and northwest. Coverage is expected to increase this afternoon compared to the past few days as a surface boundary slowly inches into the area. PWAT values are expected to rise above 2 inches (near the 90th percentile for late August at KCHS). With deep moisture rich profiles and plenty of surface heating instability values are expected to climb into the 1500 to 2000 Joules of MLCAPE which is more than sufficient for deep convection. Albeit shear is paltry at best, the influences of the upper shortwave trough should be enough to get widespread storms mainly across and west of I-95 with some multi-cellular clusters possible. Depending on how hot we get during the afternoon, surface dewpoint depressions look to range around 20 to 25 degrees and DCAPE values around 1000 to 1200 J/kg which could be supportive of damaging wind gusts with any storms that cluster up. This threat is also supported within some of the machine learning guidance showing a higher risk of damaging winds along and west of I-95 during the afternoon. As a result that portion of the area has been upgraded to a Slight(level 2 of 5) risk for severe weather with a Marginal (level 1 of 5) for the remainder of the area.

Saturday: The boundary looks to stall along or near the I-95 corridor allowing for another day of rather widespread coverage as the next shortwave overspreads the area. Scattered showers and storms look to begin throughout much of the day as subtle height falls/ascent continue over the area. This will likely keep temperatures a few degrees cooler than Friday; however, we should be able to muster up enough instability to support a more widespread round of thunderstorms during the late afternoon. Current guidance supports a little more focus over the tri county areas Saturday afternoon. The good news is that with the increased cloud cover and limited instability on Saturday, the severe risk might be a bit more marginal at best. While a strong to severe damaging wind gust cannot be ruled out, the probability of this occurring is certainly lower on Saturday than Friday. The bigger issue may become heavy rainfall as slow moving storms moving over some poor drainage areas of metro Charleston certainly raises an eyebrow. We will continue to keep an eye on this potential as confidence increases.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

21/12z TAFs: VFR conditions should prevail for much of the period with light southwesterly winds becoming southerly during the afternoon with the passage of the sea breeze. Scattered to numerous showers and thunderstorms will likely develop after 18z leading to possible reductions in vsbys and ceilings at all area terminals. PROB30s were introduced after 18z to account for this and depending on confidence in timing and coverage TEMPOs may be needed. Continued showers and storms will be possible along the coast around JZI and CHS during the overnight hours as winds become more southwesterly once again.

Extended Aviation Outlook: A front in our vicinity will bring showers and thunderstorms Saturday and Sunday, leading to occasional flight restrictions.

MARINE

Today: No significant marine concerns are expected across the local waters through today, with winds and seas remaining below Small Craft Advisory criteria. A typical summertime pattern will dominate with generally south-southwesterly flow around 10 kt and seas 2-3 ft.

Saturday through Tuesday: Outside of showers and thunderstorms, overall marine conditions will remain fairly typical for late summer, with south-southwesterly winds generally 5-15 kt with seas ranging from 2-4 ft through early next week. The main concern for mariners will be the increasing thunderstorm threat through the weekend as a front approaches and then stalls nearby.

CLIMATE

Record High Temperatures:

August 21: KSAV: 101/1902

Record High Minimum Temperatures:

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

August 24: KCHS: 76/2010

August 25: KCHS: 77/1982

CHS WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for GAZ137-216>219-238>241. SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ148>152. MARINE...None.