textproduct: Charleston

WHAT HAS CHANGED

All sections have been 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 into the weekend 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.

For today, mid-lvl ridging will remain centered across the Deep South while sfc high pressure extends across the region from the nearby Atlantic. Latest guidance supports a light west-southwest wind developing across the local area between the edge of the Atlantic high and well ahead of a cold front shifting across the Appalachian Mountains this evening, which will support warming conditions across the Southeast while large scale subsidence along with a west-northwest downsloping wind component aloft promote strong sfc heating. Latest 1000-850mb thicknesses support max temps in the mid-upper 90s away from the beaches this afternoon while mid 70 dewpts within a marine layer slowly shift onshore this afternoon along/behind a sea breeze. Some guidance indicates a potential to set new record high temperatures, see Climate section below. The combination of heat and moisture is likely to support heat index values around 105 degrees along the coastal corridor, with a few spots potentially reaching 108 degrees early afternoon. However, few to scattered showers and thunderstorms are expected to develop along/near the sea breeze with at least some clouds drifting back toward coastal areas during peak heating hours, likely limiting the potential for an extended period or large coverage of Heat Advisory level conditions. Given this expectancy, have held off on a Heat Advisory issuance this afternoon. Conditions will continue to be monitored for a short duration Heat Advisory should convection hold off or coverage be less than anticipated this afternoon.

Saturday: A similar pattern will be in place as the previous day with mid-lvl ridging extending across the Deep South and sfc high pressure attempting to hold across the western Atlantic. The day will start off warm with a south-southwest wind in advance of a front/trough with afternoon highs in the upper 90s for many areas away from the beaches. Moisture levels should become higher during peak diurnal heating with sfc dewpts in the mid-upper 70s along the coastal corridor, and heat index values are forecast to approach the 108-112 degree range. However, shower and thunderstorms developing across the local area will complicate the potential for higher heat index values, and could very well limit the potential for a Heat Advisory issuance. Conditions will continue to be monitored for max heating potential, but will largely be dependent on convective trends.

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. 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, but max temps are forecast to be a few degrees lower than the weekend. Should precip coverage be less than anticipated and/or occur late day, heat index values could approach 108 degrees along the coastal corridor.

KEY MESSAGE 2: Rain chances will increase into the weekend as we return to a more typical summertime pattern.

As a surface high pressure continues to wobble along the Florida coastline, precipitable water values of 1.6-2.0" look to remain fairly steady throughout the day, highest along the coast. A weak pre-frontal trough begins to form by the late morning, with SBCAPE values of 1500-2000 J/kg building into the early afternoon. An afternoon sea-breeze is expected push ashore and given the uncapped environment, scattered showers and thunderstorms are expected to form. Amidst the westerly surface winds the sea-breeze may struggle to push past the I-95 corridor, leading to highest chances for rain occurring near the coastline. Given the lack of shear, organized convection is not expected, which will also limit the rainfall potential of the thunderstorms as they'll likely be rather short- lived. However, given the weak flow aloft, the showers/storms will be rather slow moving, with the HREF indicating a near 50% chance for an inch of rain for areas between the I-95 corridor and the coastline across southern southeast South Carolina, decreasing to near 30% in southeast Georgia east of the I-95 corridor. Chances for showers and thunderstorms decrease into the evening hours as instability wanes.

Similar conditions are expected for Saturday ahead of an approaching cold front, with an afternoon sea-breeze interacting with 1500-2000 J/kg of CAPE likely producing another round of scattered showers and thunderstorms. Bulk shear remains on the lower end near 20 knots, but with DCAPE values near 1000 J/kg an isolated strong-severe wind gust cannot be ruled out. Expect similar chances for showers and thunderstorms for Sunday and Monday as the aforementioned front lifts to the north, with the next cold front expected to now push through on Tuesday, providing additional lift for showers and thunderstorms.

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) could result in elevated tidal departures around 1/2 ft this weekend into early next week, which sets the stage for minor coastal flooding issues 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 /06Z FRIDAY THROUGH TUESDAY/

VFR conditions will prevail at CHS/JZI/SAV terminals through 06Z Saturday. However, few to scattered showers along with a few thunderstorms could impact the terminals this afternoon, primarily at CHS and SAV terminals where a sea breeze initiates this activity during peak heating hours. All terminals carry VCTS this afternoon, mainly between 18-23Z, with PROB30 groups of TSRA and 4SM at CHS (18- 21Z) and SAV (18-22Z). By sunset, VFR conditions are expected to prevail, then persist through 06Z Saturday.

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 throughout the weekend. 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 prevail 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, with conditions remaining below small craft criteria through Saturday night. A prefrontal trough begins to form on Sunday, yielding an enhanced pressure gradient leading to winds gusts in the low 20 knot range, possibly reaching as high as 25 knots during the overnight hours into Monday and again Tuesday. A cold front is expected to move through early/middle of next week.

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.