textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section has been updated for the 12Z TAFs.

KEY MESSAGES

- 1) A prolonged heat wave will maintain hot and humid conditions for the majority of the week.

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

DISCUSSION

KEY MESSAGE 1: A prolonged heat wave will maintain hot and humid conditions for the majority of the week.

The center of a H5 595 dam ridge will remain over middle FL this afternoon, with a ridge extending northward across the Southeast U.S. today. The ridging will provide the region with very warm llvl thicknesses. An area of broad low pressure is forecast to remain over the central Carolinas this afternoon, supporting SW winds across SE GA and SC. Due to the SW winds, the sea breeze may begin an hour or two later this afternoon compared to earlier this week. Given the warm llvl thicknesses, slower sea breeze, and decent insolation, high temperatures in the upper 90s will be common this afternoon, some locations may peak at 100 degrees. However, 90th percentile guidance indicates that KCHS will likely continue the 2nd longest streak of consecutive days with temperatures <100 degrees on record, 2595 days. The record number of days in 5784 which ended 6/18/1970. The hot temperatures combined with dewpoints in the mid to upper 70s should yield heat index values greater than 108 degrees for most of the forecast area. Coastal counties of SC/GA are forecast to see heat index values to peak between 110 to 115 degrees. The dangerous heat index values will be highlighted with an Extreme Heat Warning, elsewhere a Heat Advisory will be in effect from 11 AM to 7 PM. Late afternoon thunderstorms may provide some pockets of relief from the heat.

The heat wave is expected to continue through the end of the week with heat indices likely around the 105 to 110 range and highs in the mid to upper 90s area wide. Heat products look to continue at least through Thursday and possibly into Friday with the highest probability of reaching advisory criteria mainly east of I-95 and closer to the coast including the Charleston and Savannah metro areas. While heat indices may not be as high as this afternoon, the bigger issue will be long duration heat stress mainly along the coastal areas where heat indices might not drop to below 100 degrees until well into the evening and overnight hours with lows in the upper 70s to low 80s. Several days of intense heat and minimal cooling overnight has been reflected in the HeatRisk product with widespread Major (level 3 of 4) and a corridor of Extreme (level 4 of 4) along the immediate coast Thursday and Friday. Regardless of any heat products this will continue to bring a risk of heat-related impacts, especially to those more vulnerable to heat or those without adequate cooling/hydration.

KEY MESSAGE 2: Typical summertime afternoon and evening thunderstorms this week.

Hot and humid conditions should yield moderate instability across the coastal counties once the sea breeze develops and pushes inland this afternoon into early this evening. Recent runs of the HRRR and RRFS indicated very little thunderstorm coverage this afternoon, due to dewpoint mixing well into the 60s west of the sea breeze. However, HREF does indicate isolated to scattered thunderstorms near the sea breeze this afternoon. The forecast will feature SCHC to CHC PoPs across the coastal counties during the late afternoon and evening. This pattern is expected to continue for Thursday through Saturday, with isolated coverage on Thursday and Friday.

Rain chances will likely increase Sunday into Monday as a more potent shortwave trough moves across the mid-atlantic. Expect storm coverage to increase Sunday afternoon compared to the normal summertime pattern. Storms will likely be focused along a sagging front that will slowly drift south with time. Given the increased coverage and maybe a little more deep layer flow, a couple strong to severe storms with damaging winds may be possible on Sunday.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

12Z TAFs: Terminals will remain VFR with light southwest winds this morning. Isolated to scattered thunderstorms are forecast to develop near the sea breeze this afternoon, expected to develop near or over the terminals between 20-24Z, highlighted with PROB30. In the wake of the sea breeze, winds will shift from the south-southwest with gusts near 20 kts, especially at KJZI. Convection and wind gusts should dissipated 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

Today through tonight: The pressure pattern should support south- southwest winds between 10 to 15 kts, with occasional gusts into the low 20 kts. Wave heights are forecast to favor 3 to 4 ft.

Thursday and Friday: Surges in the wake of the sea breeze may result in southwest winds to increase each afternoon and evening on Thursday and Friday. Wind gusts may peak around 25 kts, possibly requiring Small Craft Advisories. The short duration of the elevated winds should keep wave heights between 3 to 4 ft.

This weekend into Monday: The pressure pattern should support south- southwest winds between 10 to 15 kts, with occasional gusts into the low 20 kts. Wave heights are forecast to favor 3 to 4 ft.

CLIMATE

Record High Temperatures:

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

July 9: KCXM: 99/1986

July 10: KCHS: 100/1986 KCXM: 99/1986 KSAV: 102/1879

July 11: KCXM: 100/2001

July 12: KCXM: 97/1966

Record High Minimum Temperatures:

July 8: 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

CHS WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for GAZ099>101-114-115-137-216-238-240. Extreme Heat Warning 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 SCZ043-044-147. Extreme Heat Warning from 11 AM this morning to 7 PM EDT this evening for SCZ045-148>152. MARINE...None.