textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Dangerous heat and humidity will impact southeast Georgia and southeast South Carolina through the middle of the week.

DISCUSSION

KEY MESSAGE 1: Dangerous heat and humidity will impact southeast Georgia and southeast South Carolina through the middle of the week.

Today: Aloft, the forecast area will sit within the corridor of northwest flow well to the east of the large ridge centered near the Four Corners region. At the surface, the setup is rather subtle with a weakly defined boundary situated across south GA. The surface gradient will be quite diffuse which will allow the sea breeze to develop and gradually push inland. Dewpoints along and behind the front will rise into the upper 70s with high temperatures reaching well into the 90s. This setup will yield an area of heat indices into the 105-110 degree range, with the best chance of 108 and higher along the GA coast up through Beaufort County. Therefore, a Heat Advisory has been issued for this area. We could see a few isolated observations get into the 108-110 degree range across coastal Colleton and Charleston counties as well. With the boundary sagging to the south and precipitable water values dropping to less than 2 inches, model consensus is for considerably lower convection chances today. Therefore, the potential for thunderstorm development to disrupt heating and max heat index values is reduced.

Tuesday and Wednesday: A strong mid-level ridge will prevail over the Rockies and Plains into the middle of the week, with the eastern periphery building into the southeastern states. At the surface, weak high pressure will develop over the southeast. Between the ridging aloft and the weak high pressure at the surface, temperatures on both Tuesday and Wednesday will soar into the mid to upper 90s. Dew points are forecast to reach into the mid to upper 70s, highest along the coastal corridor behind the sea breeze. This set up will yield heat index values on Tuesday in the 108-113 range and Wednesday in the 105-110 range. An Excessive Heat Watch may be required for coastal locations on Tuesday and a Heat Advisory may be required on Wednesday for the same locations. Decreasing moisture on Tuesday will lead to lower precipitation chances, allowing temperatures to reach higher values for a longer duration. Afternoon showers and thunderstorms are possible on Wednesday, possibly limiting the values/duration of the heat. Heat and humidity will drop to near normal values towards the end of the week as a front approaches the region.

AVIATION /12Z MONDAY THROUGH FRIDAY/

The 12z TAF period begins with patchy fog around the area that is currently impacting both KCHS and KJZI. Solid IFR fog is in place at KJZI while the fog at KCHS is more shallow and visibilities aren't as low. This fog should mix out and dissipate pretty quickly with the onset of heating and VFR should return by ~14z. Thereafter, attention turns to thunderstorm potential in the afternoon. Overall thunderstorm coverage is expected to be less than previous days. We have maintained the PROB30 at KCHS starting at 20z. There is potential for thunderstorm impacts at KJZI and KSAV as well, though confidence is lower.

Extended Aviation Outlook: Brief flight restrictions are possible Wednesday and Thursday due to showers and thunderstorms.

MARINE

Through tonight: Overall, the gradient across the local waters will be quite weak through the period. Winds will be strongest in the afternoon and evening with the development of the sea breeze along the land/sea interface. Wind speeds should mostly top out in the 10-15 knot range during this time period. Seas are expected to average around 2 feet, but could be up to 3 feet in the outer waters.

Tuesday through Saturday: As a weak front approaches the marine waters late on Tuesday, winds and seas are forecast to surge. Wind gusts could approach 25 knots across portions of the marine waters, with the greatest chances in the offshore Charleston and 20 to 60 nm offshore GA waters. Small Craft Advisories may be required late Tuesday into Wednesday. Thereafter, marine conditions will remain below Small Craft Advisory criteria into the weekend.

CLIMATE

Record High Temperatures:

July 28: KCHS: 101/1949 KCXM: 100/1936 KSAV: 102/1949

July 29: KCHS: 100/1993 KCXM: 99/1999 KSAV: 103/1993

Record High Minimum Temperatures:

July 29: KCHS: 80/2016 KCXM: 85/1999 KSAV: 82/1878

CHS WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for GAZ137-216>219-238>241. SC...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for SCZ148-151. MARINE...None.