textproduct: Charleston

WHAT HAS CHANGED

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

KEY MESSAGES

- 1) Afternoon heat index values could climb into the 105 to 112 degree range across the I-95/coastal corridor this weekend.

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

- 3) Minor coastal flooding possible along Charleston and Colleton County coasts during evening high tides this weekend into early next week.

DISCUSSION

KEY MESSAGE 1: Afternoon heat index values could climb into the 105 to 112 degree range across the I-95/coastal corridor this weekend.

A summertime pattern will remain established across the region this weekend with mid-upper lvl ridging across the Southeast/Deep South and sfc high pressure extending across the local area from the Atlantic. Latest guidance continues to support a warm and increasingly humid setup this weekend as southerly flow advects moisture across Southeast Georgia and Southeast South Carolina while ample sunshine occurs with large-scale subsidence along with a westerly downsloping wind component along the northeast periphery of the mid-upper lvl ridge. Latest 1000-850mb thicknesses support max temps in the mid-upper 90s away from the beaches Friday and Saturday afternoons at a time when sfc dewpts increase to the mid 70s within the marine layer along the coastal corridor, supporting heat index values in the 105-110 degree range Friday afternoon and the 107-112 degree range Saturday afternoon. Should these levels of heating and humidity become realized, Heat Advisories will likely be needed across the I-95/coastal corridor of Southeast South Carolina and Southeast Georgia each afternoon this weekend. However, afternoon convection could play a role in whether these values are achieved (especially Saturday) should precip activity develop along/near a sea breeze prior to peak afternoon heating, and will need to be closely monitored for impacts on limiting heat potential this weekend. Locations further inland should experience slightly lower heat index values, mainly due to substantial mixing out of sfc dewpts where a downsloping wind component persists throughout the day.

For Sunday, shower/thunderstorm coverage along with greater cloud cover is anticipated with a front nearby and/or just inland, which should limit heat index values locally. However, warm/humid conditions remain in the forecast while the mid-upper lvl ridge attempts to hold across the Southeast to start off early next week. Should precip coverage be less than anticipated and/or occur late day, heat index values could approach Heat Advisory criteria during peak heating hours Sunday afternoon.

KEY MESSAGE 2: Rain chances will increase late this week as we return to a more typical summertime pattern.

Surface high pressure over the Mid-Atlantic states will shift offshore today into Friday while upper level ridging begins to break down. This will allow moisture to increase across the SC Lowcountry and southeastern GA, resulting in isolated to scattered showers/tstorms Friday afternoon. A cold front is then forecast to approach the region this weekend, providing an additional forcing mechanism for showers/tstorms, especially Sunday. There could be enough instability to support a few strong/severe thunderstorms Friday afternoon and into the weekend, with damaging wind gusts the main hazard.

KEY MESSAGE 3: Minor coastal flooding possible along Charleston and Colleton County coasts during evening high tides this weekend into early next week.

Breezy south-southeasterly winds post sea breeze each day along with the upcoming lunar Perigee (June 14th) and New Moon (June 15th) should result in elevated tidal departures above 1/2 ft this weekend into early next week, setting the stage for minor coastal flooding along the Charleston and Colleton County coasts during evening high tide cycles. The latest TWL forecast calls for 7.3 ft MLLW in the Charleston Harbor Saturday evening, and similar water levels are possible during evening high tides into early next week as astronomical influences peak and breezy onshore winds persist. Coastal Flood Advisories could eventually be needed.

AVIATION /12Z THURSDAY THROUGH MONDAY/

VFR conditions will prevail at CHS/JZI/SAV terminals through 12Z Friday. However, an isolated shower or thunderstorm could impact the terminals this afternoon. Confidence is too low to include in the 06Z TAF issuance.

Extended Aviation Outlook: VFR conditions should prevail at CHS/JZI/SAV terminals through the weekend, although TEMPO flight restrictions are possible with afternoon showers/thunderstorms Friday and Saturday afternoons. Chances for flight restrictions increase early next week with shower/thunderstorm coverage expanding locally ahead of an arriving cold front.

MARINE

Surface high pressure will dominate over the marine zones into Saturday. Prevailing S to SW winds generally 10 to 15 knots, with gusts to around 20 knots along the coastline each afternoon associated with the sea breeze. A cold front will approach the waters on Sunday, yielding an enhanced pressure gradient and winds surging to gusts in the low 20 knots, possibly reaching as high as 25 knots for a short time Monday afternoon.

CHS WATCHES/WARNINGS/ADVISORIES

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