textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section was updated to reflect the 12Z TAFs.

KEY MESSAGES

- 1) A prolonged heat wave will maintain hot and humid conditions through the end of the week and into the start of the weekend.

- 2) Typical summertime afternoon and evening thunderstorms this week with increasing rain chances Sunday through Tuesday.

DISCUSSION

KEY MESSAGE 1: A prolonged heat wave will maintain hot and humid conditions through the end of the week and into the start of the weekend.

Little change in the synoptic set up over the local forecast area will yield similar conditions today that were observed yesterday. The region will remain under the influence of the western periphery of a strong 594 dam high pressure over the Atlantic Ocean. At the surface high pressure will dominate over the southeastern states into the start of the weekend. Surface winds will begin each day out of the W/SW, initially limiting the inland progression of the afternoon sea breeze. This will allow temperatures to soar into the upper 90s and even 100 at some locations. Combined with dew points in the mid to upper 70s, heat index values will likely reach into the 108-112 range inland and 113-116 range along the coastal counties. A Heat Advisory remains in effect for most inland zones and an Extreme Heat Warning remains in effect for the coastal counties for today. Afternoon convection today is forecast to be isolated to scattered in coverage, limiting any potential relief from the heat. A similar forecast is in store for Friday and Saturday, although conditions look to fall just shy of Extreme Heat Warning criteria. Additional Heat Advisories are likely.

Additionally, overnight lows are only forecast to dip into the upper 70s/around 80. These warm overnight conditions could result in prolonged heat stress, especially for more vulnerable communities and those without adequate cooling overnight.

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

Today, 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 early this afternoon, pushing inland through the rest of the afternoon into early this evening. As the sea breeze pushes inland, dewpoints should rise into the upper 70s, with some values around 80. The elevated dewpoints combined with temperatures in the mid to upper 90s, moderate instability is forecast to develop across the coastal counties of SE GA/SC. Recent runs of the HRRR and HREF indicates that scattered to isolated thunderstorms developing along and near the sea breeze this afternoon and evening. Forecast soundings indicate that once storms develop, steering flow should result in the storms to track east between 15 to 20 mph. Given SBCAPE between 2500-3500 J/kg and DCAPE around 1000 J/kg, the environment may support some damaging wet microbursts. Machine learning products indicates that the greatest chance for strong to severe thunderstorms will remain along and east of the I-95 corridor. Thunderstorms coverage should steadily decrease this evening, likely ending an hour or two after sunset.

Friday and Saturday, the pattern will likely persist across the region. However, forecast soundings indicate slightly less PW and some potential dewpoints to mix a bit lower. The forecast will feature at least SCHC PoPs for sea breeze convection.

Sunday through Tuesday, GFS and ECMWF indicates that a H5 trough will ripple over the region and persist during early next week. At the sfc, a cold front is forecast to push south over the region, possibly becoming stationary. In addition, AIFS indicates that a broad sfc low may develop over the forecast area Sunday night, pushing off the coast Monday into Monday night. Forecast soundings indicate the PW will increase to 2 to 2.2" across the region. Synoptic scale forcing along with slight to moderate instability should yield much higher shower and thunderstorm coverage. These storms may potential produce pockets of excessive rainfall given the deep moisture and possible concentration of storm coverage near the coastal low. WPC has highlighted the region with a marginal risk on Sunday and Sunday night. The marginal risk could be expanded into Monday.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Prevailing VFR through the 12Z TAF period at KCHS/KJZI/KSAV. S winds will gust into the 20 knot range in the afternoon with the sea breeze at all terminals. A PROB30 line for KCHS/KSAV has been maintained to account for the risk of TSRA impacting the terminals this afternoon. Any convection should dissipate with nightfall and remain VFR through the remainder of the TAF period.

Extended Aviation Outlook: Mostly VFR. There will be a low end risk of thunderstorm impacts each afternoon and evening through Friday. Showers and thunderstorm coverage and risk of associated restrictions may increase Sunday through Tuesday.

MARINE

Today and Tonight: Little change in the pattern is expected today, with the afternoon sea breeze bringing wind gusts approaching 25 knots to the nearshore coastal waters. Opted for no Small Craft Advisory at this juncture, however it is possible that a short duration SCA could be needed for the Charleston County nearshore waters this afternoon and into this evening.

Friday into Friday Night: Surges in the wake of the sea breeze may result in southwest winds to increase during the afternoon and continue into Friday night. 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 Tuesday: 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 2 to 4 ft.

Rip Currents: A moderate risk for rip currents will remain along the Charleston County coast today and Friday. Conditions will feature 2- 3 ft swell with wave periods up to 9 seconds. In addition, SSW winds will likely generate a moderate longshore current, possibly supporting rip currents near piers and jetties.

CLIMATE

Record High Temperatures:

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 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>045-147. Extreme Heat Warning from 11 AM this morning to 7 PM EDT this evening for SCZ148>152. MARINE...None.