textproduct: Charleston

WHAT HAS CHANGED

The Aviation section has been updated for the 12z TAF issuance.

KEY MESSAGES

- 1) Above normal temperatures will prevail across the region through the weekend and into early next week. The next round of increased humidity and elevated heat indices will come this weekend and early next week as well. Heat Advisories could be needed during this time.

- 2) Summertime convection returns on Friday and is expected to persist through the holiday weekend and into next week.

DISCUSSION

KEY MESSAGE 1: Above normal temperatures will prevail across the region through the weekend and into early next week. The next round of increased humidity and elevated heat indices will come this weekend and early next week as well. Heat Advisories could be needed during this time.

Ridging aloft will remain the dominant synoptic feature across the region through the weekend and into early next week. At the surface, high pressure will extend into the region from the north today and Thursday, before a more typical subtropical high starts to take over this weekend. The position of the high today and Thursday will drive northeasterly flow across the forecast area. The result will be seasonally below normal dewpoints in the low to mid 60s for much of the area each day. Highs will still be in the low to mid 90s each day, but these low dewpoints will keep heat indices from outpacing air temperatures by much. As the subtropical high takes hold over the weekend, dewpoints will rise back into the 70s. When combined with highs creeping up into the mid to upper 90s, heat indices could rise into the 105-110 degree range for some areas. Therefore, the potential for Heat Advisories will increase over the weekend and into early next week.

KEY MESSAGE 2: Summertime convection returns on Friday and is expected to persist through the holiday weekend and into next week.

Strong ridging will be over the eastern half of the U.S. Friday morning, with a roughly 595 dam 500 mb High located to our north. This High should remain in place and gradually weaken late Friday through the holiday weekend. Surface troughing will strengthen over the Southeast U.S. Friday and persist through the holiday weekend, while High pressure is in the western Atlantic. This pattern will gradually usher more moisture into our region, with PWATs peaking in the 1.5-2" range. The combination of the weakening ridge, increasing moisture, and instability generated from above normal high temperatures should cause summertime convection to return on Friday. At this time, we only have slight chance to chance POPs for our GA counties in the afternoon, while our SC counties may stay dry. The convective coverage appears to increase on the 4th. That's when afternoon POPs are limited to a slight chance for mainly the Charleston Tri-County, while areas south into GA have up to chance POPs. Convection then increases in coverage and intensity early next week. The convective setup will vary each day, depending on how high CAPE and DCAPE values climb, if there is any shear, along with the inland movement of the sea breeze. Regardless, strong to marginally severe thunderstorms are possible each day, with the main threat being damaging winds. Locally heavy rainfall can also be expected. Convection is then expected to dissipate each evening.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

VFR conditions will prevail at KCHS, KJZI, and KSAV through 12z Thursday.

Extended Aviation Outlook: Showers and thunderstorms may bring brief flight restrictions starting Friday and persisting into the holiday weekend. Impacts are mostly likely each afternoon and evening.

MARINE

Today through tonight: Northeast flow will prevail across the local waters today and become a bit more east-northeast through the overnight. The strongest winds will come today with speeds up to around 15 knots and a few gusts up approaching 20 knots possible. Overnight, speeds will come down into the 5-10 knot range. Seas are expected to average 2-4 feet through the period.

Extended Marine: Very weak Low pressure off the Southeast Coast will yield winds from the NE, then onshore on Thursday. As the Low dissipates Thursday night, winds will generally stay onshore most of the night. Winds clock around to SE by late Friday afternoon, followed by the SW early on the 4th. Winds will then have a typical summertime pattern for the holiday weekend. This will consist of some backing during the day, with the highest winds along the land/sea interface with the formation of the sea breeze. Gusts could approach 20 kt, especially in Charleston Harbor as the sea breeze moves through. At night, expect winds to veer. Seas should stay 4 ft or less. No Small Craft Advisories are expected. Additionally, isolated to scattered convection will be possible for the holiday weekend.

Rip Currents: The combination of gusty NE, then onshore winds, along with a 2 ft swell at 9 to 10 seconds will generate a Moderate Risk of rip currents at our GA beaches today, and then again on Thursday.

CLIMATE

Record High Temperatures:

July 4: KCHS: 98/2023 KSAV: 99/1997

Record High Minimum Temperatures:

July 4: KCHS: 79/2016 KSAV: 79/1931

July 5: KCHS: 78/2017 KSAV: 78/2016

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...None.