textproduct: Charleston

WHAT HAS CHANGED

Key Message 1 and the Aviation section were updated.

KEY MESSAGES

- 1) Unseasonably hot weather with strong to severe thunderstorms will continue through at least Sunday.

- 2) Showers and thunderstorms expected to continue into early next week with a persistent 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: Unseasonably hot weather with strong to severe thunderstorms will continue through at least Sunday.

On Sunday, the H5 ridge weakens slightly across the region. At the sfc, a trough is forecast to slide east across the region, supporting winds from the WSW. The WSW winds may keep the sea breeze pinned along the coast through early afternoon, then should begin to drift inland. Similar to today, temperatures should exceed 90 degrees before noon, then peak in the mid to upper 90s by mid afternoon. The hot temperatures combined with dewpoints in the 70s should yield heat index values between 105 to 110 degrees across the coastal counties. A Heat Advisory could be needed for the coastal counties for Sunday. In addition, moderate instability and DCAPE may support another round of severe pulse-type thunderstorms. SPC has highlighted the region with a marginal risk for severe thunderstorms.

KEY MESSAGE 2: Showers and thunderstorms expected to continue into early next week with a persistent summertime pattern.

A classic early-summer pattern will remain established across southeast South Carolina and southeast Georgia through the weekend into early next week. Atlantic high pressure will remain anchored offshore while mid-lvl ridging across the western Atlantic periodically interacts with embedded shortwave perturbations rotating around the ridge periphery. Low-lvl flow remains generally south to southwest, maintaining a rich maritime tropical airmass through next week. This pattern will yield afternoon showers and thunderstorms each afternoon and evening.

Forecast soundings indicate PWAT values ranging from 1.9 to 2.3 inches through the period (near the 90th percentile for mid- June). This combined with surface dewpoints in the low to mid 70s should yield MLCAPE values between 1500-3000 J/kg amid peak heating. Mid-lvl lapse rates remain relatively modest with values ranging from 5.5-6.0 C/km, suggesting pulse-type convection will dominate through the period. Expect the afternoon seabreeze to push inland each day and collide with other outflow boundaries, yielding the primary focus for convection initiation. Weak deep-layer shear should limit storm organization, however slow storm motions between 10-15 kts combined with anomalously high moisture content will support efficient warm-rain processes.

Little change regarding the overall synoptic pattern on Monday and Tuesday as ensemble means from the GEFS and the EPS maintain subtropical ridging offshore with weak troughing across the Tennessee and lower Mississippi Valley. At the surface, a weak cold front will approach the region on Monday, and then push offshore by Tuesday evening. Convection coverage will likely increase from late morning near the coastline before expanding more inland in the afternoons. Highest PoPs will likely occur along and west of I-95 corridor where seabreeze interactions maximize.

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 6.9 - 7.1 ft MLLW in the Charleston Harbor this 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 for the Charleston and Colleton county coastlines.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

The 00z TAF period begins with VFR conditions at KCHS, KJZI, and KSAV. Remnant evening shower and thunderstorm activity looks as though it will remain away from the TAF sites. Overnight, there are no significant fog or stratus concerns. The main forecast challenge will be the potential for afternoon and evening shower and thunderstorm activity on Sunday. Current thinking is that scattered coverage right along the coast could impact the TAF sites. Therefore, we have added a PROB30 for the 18-22z time period at all 3 sites.

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

MARINE

Tonight: The pressure pattern will support southwest winds between 10 to 15 kts. Wave heights are forecast to remain between 2 to 3 ft.

Sunday through Wednesday: Expect generally south-southwesterly winds with speeds ranging from 10 to 15 kts as Atlantic high pressure persists across the local waters. A pre-frontal trough will develop on Sunday yielding an enhanced pressure gradient leading to wind gusts up to 21-23 kt (possibly 25 kt) overnight on Monday and overnight on Tuesday. Therefore, there could be need for Small Craft Advisories for portions of Monday and Tuesday regarding the elevated winds as the front advances towards the region. The cold front should pass offshore by Tuesday evening, and then rapidly move further away across the Atlantic. Seas should remain below 6 feet throughout the period.

Rip Currents: A Moderate Risk of rip currents is forecast for Sunday and Monday along the southeast South Carolina and southeast Georgia beaches given the combination of elevated winds and a lingering south-southwesterly swell.

CLIMATE

Record High Temperatures:

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

June 15 KCHS: 98/2015

Record High Minimum Temperatures:

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

June 15 KCHS: 80/2010

June 18 KCHS: 78/2015

June 19 KCHS: 79/2025 KCXM: 81/2025 KSAV: 79/1881

CHS WATCHES/WARNINGS/ADVISORIES

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