textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) A Heat Advisory is in effect for the coastal counties this afternoon and an Extreme Heat Watch is now in effect for those same counties Thursday afternoon. Additional Heat headlines will likely be required through the week and into the weekend.

- 2) Isolated to scattered thunderstorms will develop across southeast Georgia and the lower South Carolina Lowcountry, especially near the coast. One to two storms across extreme southeast Georgia may produce strong to severe wind gusts this afternoon. Additional thunderstorms are possible across portions of the region late Thursday.

DISCUSSION

KEY MESSAGE 1: A Heat Advisory is in effect for the coastal counties this afternoon and an Extreme Heat Watch is now in effect for those same counties Thursday afternoon. Additional Heat headlines will likely be required through the week and into the weekend.

Heat headlines are likely into the weekend as heat index values soar into the 100-110 range each afternoon through mid-week and upwards of 115 late in the week. The daily record highs and record high minimum temperatures will likely be challenged at our three climate sites (see Climate Section for more details). Given the very mild overnight periods and minimal coverage of precipitation, there will be few instances of relief from the heat this week and into the weekend.

Today: Ridging aloft will dominate over the southeastern states today, with high temperatures reaching into the mid 90s. With prevailing W to even NW flow at the surface the sea breeze will likely be slow to progress inland, remaining pinned at the coast into the early afternoon. However, dew points along the coastal counties are still forecast to reach into the mid 70s, yielding heat index values upwards of 110. A Heat Advisory is in effect for the coastal counties today from 11 AM to 8 PM.

Thursday and Friday: The ridging aloft amplifies towards the end of the week, likely bringing the warmest temperatures of the heat wave. Highs on each day will likely reach into the upper 90s, with a brief moment of touching 100 not out of the question. Heat index values west of I-95 will likely reach 105-108 (Heat Advisory) with locations east of I-95 reaching heat index values as high as 115. An Extreme Heat Watch is now in effect for the coastal counties for Thursday afternoon.

This Weekend: The center of ridging aloft will shift slightly westward, resulting in a slight downtick of temperatures. However, heat index values are still forecast to reach upwards of 110 along the coastal corridor likely necessitating additional Heat Advisories.

KEY MESSAGE 2: Isolated to scattered thunderstorms will develop across southeast Georgia and the lower South Carolina Lowcountry, especially near the coast. One to two storms across extreme southeast Georgia may produce strong to severe wind gusts this afternoon. Additional thunderstorms are possible across portions of the region late Thursday.

Wednesday: The center of 595 DM ridge is forecast to slide west over the northern Gulf. As a result, NW to SE heights may align over the forecast area. The mid-level flow should remain a bit chaotic due to the deep convection upstream. Satellite water vapor indicates several disturbances, some on pace to ripple over the forecast area this afternoon. Light wnw flow may keep the sea breeze pinned to the coast until mid-afternoon. Following the HREF for timing and placement of showers and thunderstorms, the forecast will feature SCT to ISO PoPs. This is much greater that coverage indicated by recent runs of the HRRR and RRFS. Given moderate instability and DCAPE between 800-1000 J/kg, one or two thunderstorms between the Altamaha and Savannah Rivers may produce strong to severe wind gusts.

Interestingly, the 0Z GFS shows an MCS tracking from the Upstate to the Coastal Plain this evening. Given the mid-level heights and lingering elevated instability, the potential for an MCS reaching the forecast area seems plausible. However, HREF and NAM12 indicates that upstream convection will dissipate before reaching the CWA.

Thursday, H5 ridge will build west over the Deep South by the afternoon and evening. Near term guidance, especially the NAM12, indicates that a well-defined shortwave will reach the forecast area late Thursday afternoon into the early evening. If this feature arrives during the heat of the afternoon, then a solid band of thunderstorms may develop across the Midlands, tracking across over the Lowcountry. At this time, the forecast will feature a band of SCHC PoPs moving west to east late Thursday afternoon.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

6Z TAFs: The terminals will remain between a broad trough across the central Carolinas and Georgia and high pressure over the western Atlantic. This pattern will yield west-southwest winds across the terminals through the TAF period. Sea breeze thunderstorms area possible at each terminal this afternoon, highlighted with PROB30 at KCHS and KJZi and TEMPO at KSAV from 20-24Z. Convection should dissipate early this evening.

Extended Aviation Outlook: Prevailing VFR.

MARINE

The pressure pattern will support southwest winds between 10 to 15 kts today, shifting from the west tonight. Wave heights are forecast to remain between 2 to 3 ft. Isolated to scattered thunderstorms may push over the nearshore waters late this afternoon and evening. One or two of these storms may produce wind gusts in excess of 34 kts, especially the nearshore GA and lower SC waters.

Thursday through Sunday: Conditions are expected to remain below Small Craft Advisory criteria this week and into the weekend. A weak coastal trough will set up across the marine waters this week, persisting into the start of the weekend. This set up will keep conditions across the marine waters breezy with southwesterly winds gusting around 15 to 20 knots. 2 to 3 ft seas are expected across the marine zones this week.

Coastal Flooding: While elevated tidal cycles are expected today due to the recent perigee and new moon, the south- southwesterly surface flow should keep tidal departures low, limiting the overall coastal flood threat. For the evening high tide this evening (occurring at 930 PM in the Charleston Harbor), tide levels look to peak around 6.7-6.8 ft MLLW, with some probabilistic guidance indicating only a 10% chance of reaching 7.1 ft MLLW.

CLIMATE

Record High Temperatures:

August 12: KCHS: 98/1957 KCXM: 98/1998 KSAV: 100/1999

August 13: KCHS: 100/1995 KCXM: 98/1913 KSAV: 98/2010

August 14: KCHS: 102/1995 KSAV: 102/1925

August 15: KCHS: 96/2023 KCXM: 99/1918 KSAV: 100/1918

August 17: KCHS: 102/1954 KSAV: 102/1954

August 18: KCXM: 97/1995 KSAV: 100/1995

Record High Minimum Temperatures:

August 12: KCHS: 79/1999 KSAV: 80/1878

August 13: KCHS: 81/2023

August 14: KCHS: 80/2023 KCXM: 83/2023 KSAV: 80/2023

August 15: KCHS: 78/1995 KCXM: 83/2021 KSAV: 80/1995

August 16: KCHS: 78/2019 KCXM: 83/2016 KSAV: 78/2019

August 17: KCHS: 80/2017 KCXM: 83/2017 KSAV: 78/2017

August 18: KCHS: 80/2017 KCXM: 82/2017 KSAV: 78/2010

CHS WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for GAZ217>219-239>241. Extreme Heat Watch from Thursday morning through Thursday evening for GAZ217>219-239>241. SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ148>152. Extreme Heat Watch from Thursday morning through Thursday evening for SCZ148>152. MARINE...None.