textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Hot and humid conditions will continue through Saturday. Isolated to scattered thunderstorms are expected this evening, and again on Saturday. A few strong to severe storms will be possible, with damaging wind gusts being the primary threat.

- 2) Rain chances and thunderstorm coverage expected to increase 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 will continue through Saturday. Isolated to scattered thunderstorms are expected this evening, and again on Saturday. A few strong to severe storms will be possible, with damaging wind gusts being the primary threat.

This Evening: Radar imagery indicates scattered convection over portions of our SC counties. This convection should wane with the setting sun, followed by a dry overnight.

Saturday: Another very hot day with widespread highs into the upper 90s (and a few triple digits) is expected. Dewpoints inland of the coast should mix out a bit, potentially into the upper 60s for much of the area and even a few mid 60s for southeast GA. Once the sea breeze begins to move inland, dewpoints will surge along with heat indices. It does appear that the potential for heat indices of 108 or higher will become increasingly confined to the coastal corridor.

Regarding thunderstorms, the coverage and environment looks similar to the last few days. Moderate instability and high DCAPE will yield an environment supportive of damaging wind gusts in the strongest storms. Convection could start in the early afternoon, but the sea breeze will be pinned closer to the coast thanks to westerly surface flow. Once a few storms develop and produce outflow boundaries, placement and strength of storms will depend on the evolution of these boundaries. Storms could continue through much of the evening until dissipating and ending by midnight and thereafter.

KEY MESSAGE 2: Rain chances and thunderstorm coverage expected to increase Sunday through Tuesday.

As noted in the previous discussion, will see a weak sfc low pressure drift across Virginia/North Carolina before ejecting into the Atlantic on Sunday. Meanwhile, it's attendant sfc cold front is expected to gradually sag southeastward across the region, resulting in increased chances for showers and thunderstorms. While model consistency still remains rather poor, there are a few models that develop another sfc low along the front, moving it across our area Sunday night then pushing offshore on Monday. If this were to happen, could certainly see a bit more moisture pool across us, and thus result in more rain - something to keep an eye on in the coming shifts. In terms of severe weather, there will still be ample instability (1500-2000 J/kg) to work with despite having cooler afternoon highs. So, like days past, can't rule out seeing a few isolated strong to severe thunderstorms, capable of producing damaging winds, small hail, and frequent lightning. With astronomical high tide of 6.44 ft MLLW occurring shortly after 7 PM, any thunderstorm activity near the Charleston peninsula will also lead to increased chances for impactful flooding.

Expect the aforementioned cold front to meander south of the region heading into the new week, keeping periodic chances for rainfall in the forecast through Tuesday. Afternoon highs during this time should also be notably cooler, as temperatures only rise into the upper 80s to low 90s. Unfortunately, this will be short lived, as a building ridge causes highs to moderate back into the low to mid 90s by the end of the week.

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

Astronomical influences 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 /00Z SATURDAY THROUGH WEDNESDAY/

00Z TAFs: KCHS and KJZI: Radar indicates scattered thunderstorms inland of these sites and approaching. Radar trends indicate impacts are more likely for KCHS than KJZI, so this is reflected with the TEMPO groups. But more amendments may be needed as radar trends change. Later this evening, the convection will end, setting up a dry, VFR night. Another round of convection and gusty winds are expected with the sea breeze late Saturday afternoon.

KSAV: VFR. Gusty winds are expected with the sea breeze late Saturday afternoon.

Extended Aviation Outlook: Shower and thunderstorm coverage, along with risks of associated restrictions, may increase Sunday through Tuesday.

MARINE

Tonight: Outside of convection, winds are gusting to around 25 kt, for the SC waters and the Charleston Harbor. The Small Craft Advisory remains in effect, but it may need to be dropped earlier depending on how convection disrupts the wind flow. Seas will mostly average 2-4 feet, but could be up to 5 ft in the Charleston County waters near the 20 nm line.

Saturday through Saturday night: Another round of elevated southwest flow, with enhancement in the afternoon and evening with the sea breeze. Winds should peak in the 15-20 knot range, with some 25 knot gusts possible in the SC waters. Conditions could become marginally supportive of a Small Craft Advisory in the Charleston County waters and possibly even Charleston Harbor. Seas should average 2-4 feet. Thunderstorms are again expected to develop inland in the afternoon and evening hours. These storms could impact the coast and the coastal waters through the evening with frequent lightning and strong wind gusts.

Sunday through Wednesday: A weak cold front to our north will slowly sag across the region Sunday into Monday, causing winds to become notably weaker. While winds look to start out westerly Sunday, should see direction gradually turn more north/northeasterly by early Monday morning. This trend is expected to continue for much of the upcoming week, with seas generally ranging from 2 to 3 ft.

Rip Currents: A moderate risk for rip currents will remain along the SC/GA coast 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 11: KCHS: 102/1986 KCXM: 100/2001 KSAV: 103/1980

Record High Minimum Temperatures:

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

July 12: KCHS: 79/2020

CHS WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory from 11 AM to 7 PM EDT Saturday for GAZ217>219- 239-241. SC...Heat Advisory from 11 AM to 7 PM EDT Saturday for SCZ045- 148>152. MARINE...Small Craft Advisory until 10 PM EDT this evening for AMZ340. Small Craft Advisory until 2 AM EDT Saturday for AMZ360.