textproduct: Charleston

WHAT HAS CHANGED

All Key Messages and sections were updated.

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.

On Friday, sfc high pressure and mid-level ridge will remain centered over the Deep South. High resolution guidance indicates that southwest winds will develop ahead of approaching cold front, timed to push over the southern Appalachians Mountains by early Friday evening. The return flow will provide the region will very warm llvl thicknesses. Some guidance indicates potential to set new record high temperatures, see Climate section below. However, NBM has been verify a bit too warm lately, so the forecast will remain below the NBM values. High temperatures may peak early in the afternoon in the mid to upper 90s. Dewpoints may surge inland behind the sea breeze, with values in the mid to upper 70s. The combination of temperatures and dewpoints may result in heat index values between 105 to 110. The challenge will be the role convection will have in cooling conditions with rainfall, cloud cover, and outflow. HREF indicates that sea breeze convection will spread at least isolated to scattered convection, beginning early in the afternoon. Storm motions would track storms toward the coast, passing over the hottest locations. Based on the marginal temperatures and convective activity, a Heat Advisory for Friday will not be issued with this package.

Saturday, temperatures will begin the day very warm, remaining near 80 degrees near the coast. Temperatures should warm rapidly after sunrise, expected to peak in the upper 90s during the afternoon. Dewpoints in the 70s should yield a larger area of heat index values of 108 or greater. A Heat Advisory could be needed. However, convection will complicate the heat index forecast for Saturday.

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 through 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 7.1 - 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 /18Z THURSDAY THROUGH TUESDAY/

18Z TAFs: VFR conditions conditions expected at CHS/JZI/SAV terminals through 18Z Friday. Showers and thunderstorms may develop near the terminals along a sea breeze near the end of the TAF period.

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. Wave heights are forecast to remain between 2 to 3 ft through Saturday night. 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, wave heights building to 2 to 4 ft.

CLIMATE

Record High Temperatures:

June 12: KCHS: 97/2016 KCXM: 97/1998 KSAV: 100/1977

June 13: KCHS: 99/2011 KCXM: 96/1998

June 14: KCHS: 99/2010 KCXM: 97/1981

Record High Minimum Temperatures:

June 11: KCHS: 76/2020 KCXM: 79/2020 KSAV: 76/2010

June 12: KCHS: 77/1986 KCXM: 80/1998 KSAV: 78/1899

June 13: KCHS: 80/2013 KCXM: 82/1998 KSAV: 80/1880

June 14: KCHS: 79/2010 KCXM: 81/2010

CHS WATCHES/WARNINGS/ADVISORIES

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