textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section was updated for the 12Z TAFs.

KEY MESSAGES

- 1) Hot and humid conditions across coastal South Carolina and Georgia today, possibly again on Saturday. Scattered thunderstorms expected to develop near the sea breeze late this afternoon into this evening. Some of these storms may become strong to severe, with localized damaging wind gusts.

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

-3) Coastal flooding is possible with the evening high tide from Sunday through Wednesday.

DISCUSSION

KEY MESSAGE 1: Hot and humid conditions across coastal South Carolina and Georgia today, possibly again on Saturday. Scattered thunderstorms expected to develop near the sea breeze late this afternoon into this evening. Some of these storms may become strong to severe, with localized damaging wind gusts.

Today, a sfc trough is forecast to remain over the central Carolinas this afternoon, supporting WSW winds across SE GA and SC. Due to the WSW winds, the sea breeze may remain pinned along the coast, then pushing inland late this afternoon into early this evening. As the sea breeze pushes inland, dewpoints should rise into the upper 70s, with some values around 80. Temperatures along and ahead of the sea breeze should peak in the upper 90s by mid afternoon. The hot temperatures combined with the elevated dewpoints should result in a corridor of heat index values between 106 to 113 degrees. An Extreme Heat Warning will remain in effect for Charleston and tidal Berkeley Counties from 11 AM to 7 PM. A Heat Advisory will highlight the area from Dorchester County south across the coast of SC and GA. Similar heat index values are possible over the same areas on Saturday.

The hot and humid conditions will likely yield moderate instability across the coastal counties of SE GA/SC. Recent runs of the HRRR, RRFS, and HREF indicate that scattered to isolated thunderstorms developing along and near the sea breeze late this afternoon and evening. Forecast soundings indicate that once storms develop, steering flow should cause the storms to track east between 15 to 20 mph. Given SBCAPE between 2500-3500 J/kg with pockets of 4000 J/kg and DCAPE around 1000 J/kg, the environment may support some damaging wet microbursts. Machine learning products indicate that the greatest chance for strong to severe thunderstorms will remain along and east of the I-95 corridor, favoring areas along and north of the Savannah River. SPC generally highlights the same area with Marginal Risk for damaging wind gusts. Thunderstorms coverage should steadily decrease by mid evening, with storms pushing offshore.

KEY MESSAGE 2: Typical summertime afternoon and evening thunderstorms this weekend, with increasing rain chances Sunday through Tuesday.

Saturday: Amidst the continuing hot and humid conditions, rainfall chances will remain isolated to scattered. H500 heights remain quite consistent, with the diurnal sea-breeze expected to be the main trigger for afternoon convection. Similar to Friday, expect 1500- 2500 J/kg of CAPE to build into the afternoon hours, with shear generally remaining unimpressive at near 20 knots. With precipitable water values remaining in the 1.5-2 inch range and DCAPE values near 1000 J/kg, strong damaging winds remain the primary risk.

Sunday - Tuesday: While the Atlantic surface high pressure continues, weak H500 troughing to our north will bring a weak surface low pressure off the Virginia/North Carolina coast and into the Atlantic on Sunday. A weak cold front associated with the surface low will slowly sag down into the region, bringing increased chances for showers and thunderstorms to the region. While agreement amongst the models is not high, a few models continue to depict a weak surface low pressure developing along the cold front, moving across the area Sunday night before pushing offshore on Monday. Despite slightly cooler temperatures, with highs expected to fall into the lower/mid 90s, 1500-2000 J/kg of CAPE will continue isolated chances for strong-severe thunderstorms. With astronomical high tide of 6.44 ft MLLW occurring shortly after 7 PM, any thunderstorm activity near the Charleston peninsula will increase chances for impactful flooding.

Cooler air continues to filter down into the region as a surface high pressure moving towards/across the Appalachians, with the front remaining across/south of the region continuing periodic chances for rainfall on Monday and Tuesday. This will bring temperatures down into the mid/upper 80s on both days. H500 heights begin to rise again on Wednesday as the ridge strengthens, with temperatures rising back up into the lower 90s.

KEY MESSAGE 3: Coastal flooding is possible with the evening high tide from Sunday through Wednesday.

Astronomical forces on tides will increase early next week, with a lunar perigee on Monday and a New Moon on Tuesday. Minor coastal flooding is possible across Charleston and coastal Colleton Counties Sunday evening. Coastal flooding may increase Monday through Wednesday with rising astro tides and onshore winds. In addition, rainfall may overlap with the evening high tide cycles, see Key Message 2 for additional details.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

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 TEMPOs at KCHS and KJZI and PROB30 until 2Z at KSAV. As the sea breeze develops, winds will develop gusts between 20 to 25 kts, especially at KCHS and KJZI. Convection and wind gusts should push offshore this evening.

Extended Aviation Outlook: There will be a low end risk of thunderstorm impacts Saturday afternoon and evening. Shower and thunderstorm coverage, along with risks of associated restrictions, may increase Sunday through Tuesday.

MARINE

Today into tonight: The sea breeze will likely trigger scattered thunderstorm across the coast late this afternoon. These storms are forecast to push over the Atlantic waters through early this evening. Some of the storms may yield gusty winds, requiring Special Marine Warnings.

Surges in the wake of the sea breeze may result in southwest winds to increase during this afternoon and continue into tonight. 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. Winds should start to diminish after midnight.

Saturday into Wednesday: Atlantic surface high pressure will continue to support south-southwest winds between 15 to 20 knots, with occasional gusts into the lower-mid 20s on Saturday. While wave heights are forecast to favor 3 to 4 ft, a short-lived Small Craft Advisory cannot be ruled out, especially along the nearshore waters from South Santee to Edisto Beach. Sunday into Monday is expected to see a weak cold front sag into the region from the north, bringing weaker westerly winds on Sunday becoming north-northeasterly Monday morning. Surface flow looks to become variable later on Monday, with a surface high pressure moving in from the north on Tuesday switching winds around to become out of the northeast.

Rip Currents: A moderate risk for rip currents will remain along the SC/GA coast today and Saturday. 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 10: KCHS: 100/1986 KCXM: 99/1986 KSAV: 102/1879

July 11: KCHS: 102/1986 KCXM: 100/2001 KSAV: 103/1980

Record High Minimum Temperatures:

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 GAZ217>219-239-241. SC...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for SCZ044-045-148-149-151. Extreme Heat Warning from 11 AM this morning to 7 PM EDT this evening for SCZ150-152. MARINE...None.