textproduct: Charleston

WHAT HAS CHANGED

All sections.

KEY MESSAGES

- 1) Rain chances will increase late this week as we return to a more typical summertime pattern.

- 2) Afternoon heat index values could climb into the 105 to 110 degree range across the I-95/coastal corridor this weekend.

DISCUSSION

KEY MESSAGE 1: Rain chances will increase late this week as we return to a more typical summertime pattern.

The sfc high pressure over the Mid-Atlantic will shift offshore Thursday into Friday and the upper level ridging will begin to break down. This will allow moisture to increase across the Southeast while also decreasing the large scale subsidence, resulting in isolated to scattered showers/tstorms Thursday into Friday. A cold front is then forecast to approach the region this weekend, providing an additional forcing mechanism for showers/tstorms. There could be enough instability to support a few strong/severe thunderstorms Friday afternoon and into the weekend.

KEY MESSAGE 2: Afternoon heat index values could climb into the 105 to 110 degree range across the I-95/coastal corridor this weekend.

A classic early-summer pattern will remain established across southeast South Carolina and southeast Georgia through the weekend as mid-lvl heights gradually rise beneath a strengthening western Atlantic ridge. This pattern will yield south-southwesterly flow, allowing for a good amount of tropical moisture to advect into the region. The most recent ensemble guidance indicates increased probabilities for heat indices exceeding 100F across the I-95/coastal corridor this weekend.

Friday: The region will remain on the western periphery of the Atlantic ridge with temperatures climbing into the mid to upper 90s away from the beaches. Expect dewpoints to remain in the mid to upper 70s owing to continued maritime moisture transport from the Atlantic and the Gulf. This will yield afternoon heat index values between 100F and 108F, with the highest values across the I-95/coastal corridor. These values will likely approach and/or meet Heat Advisory thresholds (i.e. values between 108F to 112F for at least 2 hours). While scattered seabreeze-driven convection is expected in the afternoon, storm coverage should remain insufficient to provide widespread relief from the heat. If any convection develops, it will be capable of briefly lowering the temperatures, however it will also reinforce the already very humid environment.

Saturday: The hottest conditions are expected on Saturday as the ridge briefly strengthens across the region. Expect afternoon temperatures to climb into the upper 90s to low 100s away from the beaches. This combined with dewpoints in the mid to upper 70s should favor afternoon heat index values between 104F to 110F (highest across the I-95/coastal corridor). Again, these values will likely approach and/or meet Heat Advisory thresholds and the scattered seabreeze-driven convection will likely not provide widespread relief from the heat.

Sunday: Attention turns towards an approaching cold front advancing southeastward from the Appalachians and Tennessee Valley on Sunday. Although it'll remain warm and humid out ahead of the front, increasing cloud cover combined with higher probabilities of showers and thunderstorms will likely limit daytime heating compared to Friday and Saturday. This will still yield heat index values in the 100F to 107F range before convection develops, but widespread values above 108F appear less likely.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Prevailing VFR through the 18Z TAF period at KCHS/KJZI/KSAV.

Extended Aviation Outlook: VFR conditions are expected to prevail at CHS/JZI/SAV terminals. However, brief flight restrictions are possible with afternoon showers and/or thunderstorms Thursday through Monday.

MARINE

Prevailing S to SW winds expected through early next week. The gradient could be slightly enhanced due to a cold front approaching from the northwest. Sustained winds could be 15-20 kt at times. A slight sea breeze enhancement will occur along the coast each afternoon.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...None.