textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section was updated for the 12Z TAF issuance.

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.

Mid to upper level ridging will dominate over the southeastern states today, while at the surface high pressure will prevail over the Mid-Atlantic states. Between the high pressure at the surface and the resulting drier air aloft from the upper level ridging, a mostly dry forecast has been maintained. 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 SC Lowcountry and southeastern GA, 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.

The pattern will remain summer-like late week with mid-upper lvl ridging across the Southeast/Deep South and sfc high pressure extending across the western Atlantic. Latest guidance suggests a light southerly flow advecting higher dewpts across the local area while ample sunshine associated with large-scale subsidence and a downsloping wind component develops along the northeast periphery of the mid-upper lvl ridge. Hot and humid conditions are expected during the upcoming weekend with latest 1000-850 mb thicknesses supporting max temps in the mid/upper 90s away from the beaches Friday and Saturday afternoons. However, the placement of highest heat index values will be dependent on how much mixing out of sfc dewpts occurs across the interior where the downslope wind prevails and the arrival of showers/thunderstorms, which are primarily diurnally driven and perhaps initiated along a sea breeze during afternoon hours. Low-lvl moisture convergence closer to the coast along with marine layer influences likely maintains higher sfc dewpts in the mid-upper 70s during the weekend, which could support heat index values as high as 105-110 degrees should afternoon convection arrive late day and/or precip coverage is more sparse during peak diurnal heating. Heat Advisories could eventually be needed this weekend, particularly across the coastal corridor if convection holds off until maximum daytime heating takes place.

On Sunday, shower/thunderstorm coverage along with greater cloud cover is anticipated with the arrival of a cold front, which should limit heat index values locally. However, warm/humid conditions will continue to be monitored as the potential for 103-108 degree heat index values still remains locally should the front be delayed and/or precip coverage becomes less than currently anticipated early next week.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Prevailing VFR through the 12Z 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 Sunday.

MARINE

Today and Tonight: Quiet marine conditions are expected with Atlantic high pressure holding across local waters. Southerly winds should top out around 15 kt, strongest along the land/sea interface where a sea breeze circulation develops. Seas will range between 2-3 ft.

Thursday through Sunday: A typical summertime pattern holds across local waters through late week with Atlantic high pressure in place. South to southwest winds should top out in the 15-20 kt range, highest near the land/sea interface where a sea breeze circulation occurs each late morning/afternoon. Seas should generally range between 2-3 ft. A cold front should then approach the region early next week, which could result in a slight uptick of southerly winds as the pressure gradient tightens. Wind gusts should fall just short of Small Craft Advisory criteria. Seas should slowly build to 3-4 ft early next week as well.

CHS WATCHES/WARNINGS/ADVISORIES

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