textproduct: Charleston

WHAT HAS CHANGED

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

KEY MESSAGES

- 1) Unseasonably hot weather will continue through at least Sunday.

- 2) Daily coverage of showers and thunderstorms expected to increase through the weekend and into next week as a more typical summertime pattern returns to the region.

- 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 will continue through at least Sunday.

Deep westerly flow will persist today, maintaining oppressively hot temperatures across the area. The sea breeze will only slowly creep inland during the afternoon. Farther inland, relatively dry air aloft should mix down, with surface dewpoints in the upper 60s to lower 70s for much of the afternoon. The coastal corridor is expected to see upper 90s temps overlap with mid to upper 70s dewpoints, where heat indices could reach 105-110F for a few hours. The one question mark is how quickly diurnal convection spreads cold pools and potentially drops the temps over a substantial area. There were quite a few spots that reached criteria on Friday, and today looks like a similar pattern. We issued a Heat Advisory for the coastal zones but also included all of Berkeley County, until 5pm.

Sunday will continue the heat wave, with potentially a slightly larger area of Heat Advisory criteria if the sea breeze makes it farther inland. We should, however, have pretty good afternoon convection coverage as a lee trough strengthens.

KEY MESSAGE 2: Daily coverage of showers and thunderstorms expected to increase through the weekend and into next week as a more typical summertime pattern returns to the region.

Through the weekend and into next week, the pattern across southeast GA and southeast SC will gradually shift toward a typical summertime pattern supportive of showers and thunderstorms each day. Aloft, the ridging that has been in place for the last several days will break down and be replaced by a more zonal flow through Sunday. At the surface, a weak front/trough is expected to drift into the vicinity Saturday and Sunday before lifting to the north. Overall thinking remains unchanged in that today and Sunday will result in a modest increase in convective coverage, given plenty of instability and an afternoon sea-breeze expected each day.

Similar to what was observed on Friday, mid-level flow will remain on the weak side throughout the weekend, resulting in storm motions of only 10-15 knots. Given precipitable water values remaining near 2 inches, locally heavy rainfall will again be a possibility today and Sunday. The aforementioned front/trough looks to setup just east of the I-95 corridor today, with additional lift provided by an afternoon sea-breeze, and will together act as a focus for shower and thunderstorms development this afternoon. For areas that see rain today, HREF probabilities for an inch are as high as 70%, with probabilities for 3 inches on the low end at 10%. Probabilities drop to isolated 50% chances on Sunday, likely due to marginally faster storm motions.

Given weak shear, pulse showers and thunderstorms will continue to remain the primary thunderstorm type today and Sunday. SBCAPE values of 1500-2000 J/kg will allow for storms to grow quickly, possibly producing small hail in its initial stages as was observed on Friday (though freezing levels are a smidge higher), before falling apart relatively quickly and transitioning to a damaging wind threat as DCAPE values remain near 1000 J/kg before dissipating.

As we head into the early and middle part of next week, large and broad troughing is expected to encompass the eastern half of the CONUS. This will likely result in a more significant increase in coverage in the early to middle part of next week due to the combination of the presence of the trough aloft and an approaching cold front, with some models stalling the front across the area before washing it out into the middle of next week, with others pushing it through though warm temperatures remain.

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 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 for the Charleston and Colleton county coastlines.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

12Z TAFs: VFR conditions expected for the remainder of the morning hours with light southwesterly winds. Similar to Friday, scattered showers and thunderstorms are expected this afternoon and evening, likely producing TEMPO flight restrictions at times, and have thus included PROB30 groups at all TAF sites. Guidance has hinted at storms may develop an hour or two later than initially expected, so have pushes the PROB30s back an hour at CHS and JZI. The overnight period into Sunday will see the return of VFR conditions.

Extended Aviation Outlook: VFR conditions should prevail at CHS/JZI/SAV terminals on Sunday, 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 today. S to SW winds will remain close 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 Sunday morning. A prefrontal trough begins to form on Sunday, yielding an enhanced pressure gradient leading to wind 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 into the vicinity during the early/middle part of next week, continuing chances for breezy winds, though seas look to remain below 6 feet.

CLIMATE

Record High Temperatures:

June 13 KCHS: 99/2011 KCXM: 96/1998 KSAV: 102/2011

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

June 15 KCHS: 98/2015

Record High Minimum Temperatures:

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

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...Heat Advisory from 11 AM this morning to 5 PM EDT this afternoon for GAZ217-219-239-241. SC...Heat Advisory from 11 AM this morning to 5 PM EDT this afternoon for SCZ045-148>152. MARINE...None.