textproduct: Charleston

WHAT HAS CHANGED

Updated the Aviation Section for the 12Z TAFs and Marine Section.

KEY MESSAGES

- 1) Heat and humidity will continue across southeast Georgia and the South Carolina Lowcountry today. Strong to severe thunderstorms are possible along and east of I-95 this afternoon and evening. Heavy downpours could lead to pockets of excessive rainfall.

- 2) Hot and humid conditions will persist through much of the week.

- 3) Typical summertime afternoon and evening thunderstorms this week.

DISCUSSION

KEY MESSAGE 1: Heat and humidity will continue across southeast Georgia and the South Carolina Lowcountry today. Strong to severe thunderstorms are possible along and east of I-95 this afternoon and evening. Heavy downpours could lead to pockets of excessive rainfall.

Debris clouds from convection last evening are expected to gradually dissipate and drift north through the pre-dawn hours. Thin cloud cover should allow for decent insolation this morning. Much like the past several days, temperatures should generally exceed 90 degrees by noon, then peaking in the mid to upper 90s this afternoon. The hot temperatures combined with dewpoints in the mid to upper 70s along the coast will yield heat index values between 105 to 110. A Heat Advisory is in effect from 11 AM to 7 PM.

The hot and humid conditions should once again produce moderate instability along the coast. SBCAPE values over portions of the coastal counties may exceed 3500 J/kg during the heat of the afternoon. The forecast area will remain between a closed H5 low centered over the middle MS Valley and H5 593dam ridge over the Bahamas. Shear between the sfc to H5 is weak, but is notably greater than the past couple of days. 0Z HREF indicates that convection will develop over the coastal counties of SC/GA beginning early this afternoon. Some storms along and east of I-95 will likely develop strong updrafts with storm tops around 50 kft. Collapsing water- loaded updrafts may yield localized areas of damaging wind gusts. SPC has highlighted portions of the SC Lowcountry with a 5% risk of damaging wind gusts, lining up well with some ML products. A few Severe Thunderstorm Warnings may be needed this afternoon and evening. In addition, storm motions around 10 mph and PW around 2.2 inches will likely lead to swaths of heavy rainfall of 2-3 inches. Flood Advisories may be needed for some coastal SC/GA counties, including Berkeley County.

KEY MESSAGE 2: Hot and humid conditions will persist through much of the week.

Upper ridging will maintain control over the region through much of the week, leading to a continued stretch of above normal temperatures. Highs are forecast to peak in the mid to upper 90s each day, with heat indices of 100+. Areas east of I-95 and closer to the coast will see the highest heat indices, generally averaging in the 107-113F range as dewpoints surge into the upper 70s/near 80 with the sea breeze. Additional Heat Advisories or Extreme Heat Watch could be needed for the coastal corridor, including much of the Savannah and Charleston Metro Areas, for Wednesday and Thursday. Little relief is expected overnight with lows only falling to the upper 70s/lower 80s over most locations. See climate section below for potential records in jeopardy. NWS HeatRisk currently shows a Major (level 3/4) HeatRisk each day, so regardless of heat product issuance, this extended stretch of hot and humid conditions will bring a risk of heat-related impacts, especially to those more vulnerable to heat or those without adequate cooling/hydration.

KEY MESSAGE 3: Typical summertime afternoon and evening thunderstorms this week.

The region will be situated between high pressure offshore and a trough of low pressure inland through much of the week, with ridging the primary feature aloft. Larger scale forcing is lacking, but isolated to perhaps scattered showers and thunderstorms will be possible each day largely due to daytime heating and mesoscale boundaries like the sea breeze. Coverage will be highest in the afternoon and early evenings, before dwindling after sunset with loss of insolation. While the environment favors mainly pulse-type convection, a couple strong to severe storms with damaging wind gusts cannot be ruled out. Locally heavy rainfall is also possible with any storms, but flooding risk is low especially given the hot and dry conditions of late.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

12Z TAFs: Terminals will remain VFR with light southwest winds this morning. Scattered thunderstorms are forecast to develop near the sea breeze this afternoon, expected to develop near or over the terminals between 20-24Z. The KCHS and KSAV TAFs will feature a TEMPO for gusty winds and -TSRA, with a PROB30 at KJZI. Convection should dissipate early this evening.

Extended Aviation Outlook: There will be a risk for tstm impacts at the terminals each afternoon/evening, especially at KCHS and KSAV.

MARINE

Early this morning: At sunrise, National Weather Service Doppler Radar detected clusters of showers and thunderstorms over portions of the near and outer Atlantic waters off the Charleston County coast. These showers and thunderstorm were likely developing along a land breeze, which should continue to trigger showers and storms into the early daylight hours. The environment this morning may support the development of waterspouts near these showers and thunderstorms.

Today through tonight: This afternoon and evening, strong thunderstorms may slide off the GA/SC coast. Some of these storms may require Special Marine Warnings. Otherwise, the pressure pattern should support south-southwest winds between 10 to 15 kts, with occasional gusts to 20 kts. Wave heights are forecast to favor 3 to 4 ft.

Wednesday through Sunday: Not much change in the pattern this week, with southwest winds in the morning backing more to the south for the afternoon and evenings. Gusts will largely top out in the low 20 kt range, but later in the week, there is a greater chance at seeing some 25 knot gusts. Seas will average 2-5 feet.

CLIMATE

Record High Temperatures:

July 8: KCHS: 100/2016 KSAV: 101/2010

July 10: KCHS: 100/1986 KCXM: 99/1986

July 11: KCXM: 100/2001

July 12: KCXM: 97/1966

Record High Minimum Temperatures:

July 7: KCHS: 80/2017 KCXM: 82/2022 KSAV: 80/1883

July 8: KCHS: 82/2016 KCXM: 83/2016 KSAV: 80/1990

July 9: KCHS: 80/1998 KCXM: 85/1998 KSAV: 80/1883

July 10: KCHS: 81/1986 KCXM: 82/1986

July 11: KCHS: 80/2016 KCXM: 82/2016

July 12: KCHS: 79/2020 KCXM: 82/1998

CHS WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for GAZ217>219-239-241. SC...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for SCZ045-148>152. MARINE...None.