textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) An isolated strong to severe thunderstorm will be possible late this evening, mainly for southeast South Carolina. The primary threat will be damaging wind gusts.

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

DISCUSSION

KEY MESSAGE 1: An isolated strong to severe thunderstorm will be possible late this evening, mainly for southeast South Carolina. The primary threat will be damaging wind gusts.

Aloft, the forecast area will continue to sit within the corridor of northwest flow on the far eastern periphery of the large ridge positioned near the Four Corners region. This larger scale flow pattern will help to push a developing MCS across the OH Valley into the central and southern Appalachians after sunrise. This convection is then expected to continue progressing to the south and southeast through the morning while interacting with the high terrain of the western Carolinas. The initial convection should then weaken and dissipate into the afternoon. The concern for our forecast area will come later into the evening, primarily for southeast SC. If some convection could survive, or if new convection can initiate, the ambient environment could be supportive of a few strong to severe storms capable of producing damaging wind gusts. Current thinking is that the threat isn't particularly high thanks to the timing and loss of peak heating by that time. Also, all hi-res model solutions and the 28/00z HREF depict very little activity through the evening and into the early morning hours. However, until the initial upstream convection develops and gets properly initialized by hi-res models the potential remains.

KEY MESSAGE 2: Dangerous heat and humidity will impact southeast Georgia and southeast South Carolina through the middle of the week.

Today is expected to be hot and humid across all of southeast GA and southeast SC. High temperatures are forecast to peak in the mid to upper 90s, with a few triple digits possible across southeast GA along and south of I-16. With dewpoints at least in the low to mid 70s everywhere, heat indices of up to 108 degrees will be quite common. The most uncomfortable conditions are expected along the coastal corridor, where dewpoints will likely surge into the upper 70s behind the sea breeze. This should yield heat indices into the 110-112 degree range for several hours in the afternoon. There is even potential for a few areas to see heat indices over 112 (Extreme Heat Warning criteria) for a brief period of time. Current thinking is that the duration of these higher heat indices will be short and that the best course of action is to maintain the ongoing Heat Advisory for the entire forecast area.

One potential fly in the ointment is the potential for cloud cover to keep temperatures from reaching the expected potential. Within the northwest flow aloft, a steady stream of mid/high clouds associated with upstream convection could be a bit more opaque than expected and sufficient to keep highs a few degrees lower than forecast.

Wednesday: A strong mid-level ridge will prevail over the Rockies and Plains, 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 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 105-110 range. A Heat Advisory may be required across portions of the forecast area, especially the coastal corridor. One complicating factor will be the chances for afternoon convection. Models are not in good agreement regarding the degree of coverage. The current forecast features PoPs in the 25-35% range, but if this trends wetter with future updates the threat for a Heat Advisory would decrease. Heat and humidity will drop to near normal values towards the end of the week as a front approaches the region.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

The 06z TAF period begins with VFR conditions at KCHS, KJZI, and KSAV. Winds will be southwest through the morning and into the afternoon ahead of the sea breeze. Behind the sea breeze, winds will turn more southerly with gusts into the 15-20 kt range possible through the evening. Overall, thunderstorm chances are expected to be low tomorrow afternoon. The main chance of shower and thunderstorm impacts will come late in the evening at KCHS and KJZI. For now, these chances look too low to include any mention in the TAF's.

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

MARINE

Today and Tonight: A weak front will approach the region today, yielding an increase in both winds and seas this evening into tonight. A Small Craft Advisory has been issued for the Charleston County nearshore waters and the 20 to 60 nm offshore GA waters. Conditions within the Charleston Harbor will need to be monitored for a possible short-duration Small Craft Advisory as gusts could approach 25 knots this afternoon and evening.

Wednesday through Sunday: Winds and seas will decrease Wednesday morning to below Small Craft Advisory criteria. Southeasterly flow will dominate across the marine waters through the weekend, with gusts topping out around 10 to 15 knots through Friday. Gusts are forecast to shift to the SW and increase to 15 to 20 knots this weekend as a cold front approaches the region.

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 8 PM EDT this evening for GAZ087-088-099>101-114-115-137-216>219-238>241. SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ040-042>045-147>152. MARINE...Small Craft Advisory from 6 PM this evening to 8 AM EDT Wednesday for AMZ360-384.