textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Isolated strong to severe thunderstorms possible this afternoon and evening and again Tuesday evening. 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: Isolated strong to severe thunderstorms possible this afternoon and evening and again Tuesday evening. The primary threat will be damaging wind gusts. Areas outside the thick cirrus

This afternoon: Satellite water vapor showed a shortwave near the AL/GA line, tracking towards the ESE. Visible satellite showed band of thick cirrus east of the disturbance across the SC Lowcountry and portions of SE GA. Areas outside the thick cirrus, primarily along and south of the Savannah River have warmed to the convective temperature and cumulus field has developed. SPC mesoanalysis indicates that MLCAPE across SE GA and portions of SC has increased to 3000 J/kg. In addition, DCAPE values across the region should remain around 1000 J/kg. Given the approach of the shortwave and the moderate instability, it appears that isolated strong to severe thunderstorms are possible this afternoon and evening, primarily over the Savannah River border counties. Wind gusts will be the greatest concern with the tallest storms.

Tuesday evening into early Wednesday morning: High resolution guidance indicates that a squall line will develop over NC ahead of cold front Tuesday afternoon. This line should track rapidly to the SE, with the southern portion of the line expected to reach the CHS Tri-county during the evening hours. These storms may not arrive over Berkley and Dorchester Counties until after sunset Tuesday evening. Instability across the forecast should begin to decrease in storms should decrease in intensity. However, if storms outpace the guidance, then the risk of severe weather will increase significantly. At this time, one or two of these storms may remain organized with decent structure, these storms could produce swaths of strong to damaging wind gusts.

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

Muggy conditions continue to prevail across the region, despite increasing cloud cover, with latest observations showing temperatures in the upper 80s to mid 90s and dewpoints into the mid to upper 70s. As a result, have seen heat index values nearing 110 degrees, especially across our far southeastern Georgia counties. Given that there is a potential for showers and storms further inland this afternoon, think the overall extent and duration of higher heat indices further north and inland will remain rather limited. Thus, believe the current Heat Advisory, set to expire at 7 PM, remains in good shape.

Tuesday and Wednesday: Strong mid-level ridging continues over the Rockies and Plains through mid-week, with the eastern periphery building into the southeastern CONUS. Meanwhile, at the sfc, will also see a weak high pressure develop over the southeast, causing oppressive heat to persist. In regard to temperatures, currently have highs soaring into the mid to upper 90s and dewpoints in the mid to upper 70s, with the highest values occurring along the coastal corridor behind the sea breeze. With minimal precipitation chances in place, believe heat index values up to 110 degrees will prevail long enough in both extent and duration to warrant headlines. Thus, after collaboration with neighbors, have issued an area wide Heat Advisory that will be in effect Tuesday between 11-7 PM. We encourage folks to stay hydrated, take frequent breaks in the shade or AC, and to check on vulnerable populations like children and elderly.

Similar conditions look likely Wednesday, though an advancing front may possibly limit the extent/duration of heat. For now, have afternoon highs in the mid to upper 90s and dewpoints in the low to mid 70s, with the highest occurring along the coastal corridor again. Will continue to monitor trends in regard to the aforementioned front, but additional headlines may eventually be needed as heat index values approach 110 degrees.

AVIATION /18Z MONDAY THROUGH SATURDAY/

18Z TAFs: As noted in the previous discussion, could see some showers and storms develop this afternoon across our area. While coverage is expected to remain much more limited than days past, have continued to carry TEMPO groups at all TAF sites between roughly 19-23Z. Outside of this, should see VFR conditions and light and variable winds prevail. Direction then turns more southwesterly by the end of the period.

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 this 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 front approaches the marine waters late on Tuesday night into Wednesday morning, winds and seas are forecast to surge. Wind gusts could approach 25 knots across portions of the marine waters, with the greatest chances between 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 to 8 PM EDT Tuesday for GAZ087-088- 099>101-114-115-137-216>219-238>241. Heat Advisory until 7 PM EDT this evening for GAZ137-216>219- 238>241. SC...Heat Advisory from 11 AM to 8 PM EDT Tuesday for SCZ040- 042>045-147>152. Heat Advisory until 7 PM EDT this evening for SCZ148-151. MARINE...None.