textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section has been updated for the 00Z 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 Heat Advisories could be needed.

- 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 Heat Advisories could be needed.

Ridging aloft will remain the dominant synoptic feature through the week and into the holiday weekend. At the surface high pressure will extend into the region from the north, resulting in north to northeasterly flow at the surface. While this synoptic set up will yield above normal temperatures, with highs forecast in the low to mid 90s, the northeasterly flow will advect lower dew points into the region. The lower dew points will help keep heat index values held down, generally in the upper 90s to around 100 today through Thursday. Friday and heading into the holiday weekend subtropical high pressure off the southeast coast will strengthen, driving a more typical southwesterly surface flow. This will allow dew point to rise to normal values for early July. The combination of the increasing dew points and high temperatures remaining in the mid to upper 90s will yield heat index values in the 105 to 110 range. Heat Advisories may be required for portions of the forecast area through the holiday weekend.

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

As the aforementioned ridge begins to weaken as it continues eastwards, a weak surface trough will set up along the coast as surface high pressure develops over the western Atlantic. With flow aloft increasingly getting an eastward component, low-mid level moisture will steadily increase into the weekend. Between the previously mentioned surface trough and the expected afternoon sea breeze, the return for daily scattered showers and thunderstorms is therefore expected, primarily in the afternoon hours with storm coverage waning into the evening. Given daily instability values climbing into the 2-3k J/kg range, strong to severe thunderstorms can't be ruled out. However, with the lack of shear, organized convection is not expected with mostly cold- pool driven storms to monitor. Given PWATs as high as 1.5-2.0", locally heavy rainfall can also be expected.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

VFR conditions will prevail at CHS/JZI/SAV terminals through 00Z Thursday. East-southeast winds could gust up to 15-20 kt at all terminals Thursday afternoon during and post sea breeze.

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

Tonight: The local waters are situated between an area of low pressure to the east and high pressure inland, creating northeasterly flow across the region. Observations show mostly 10-15 knots of sustained flow, and with a few gusts up into the lower 20s, with perhaps a few gusts into the mid 20s across the waters from Edisto, SC to Savannah, GA as the pressure gradient maxes out this afternoon. Overnight, winds will be a bit more out of the east-northeast, with speeds around 15 knots. Seas will tick upward a bit, and average 2-4 feet for most of the period.

Extended Marine: Very weak low pressure off the Southeast Coast will yield winds from the NE or E through Thursday, with a surface high pressure slowly shifting toward the coast from the east-central CONUS. As the low further weakens and dissipates into Thursday night, winds will become southeasterly on Friday. Afterwards, surface high pressure will again build across the Atlantic region and become the dominant feature. This will swing winds around to become out of the southwest by early Saturday, becoming south- southeasterly throughout the afternoon. Winds are expected to remain largely below small craft criteria, with highest chances for short- lived gusts into the mid 20s occurring behind the expected afternoon sea-breezes.

Renewed chances for scattered showers and thunderstorms return to the waters Thursday afternoon. A typical summertime pattern continues into the weekend, bringing daily chances for scattered showers and thunderstorms.

Rip Currents: The combination of gusty NE winds and a 2 ft swell at 9 to 10 seconds will generate a Moderate Risk of rip currents at Charleston County and southeastern Georgia beaches, while a slightly more onshore flow will keep beaches from Edisto, SC to Savannah, GA in the Low Risk. For Thursday, 3 ft/9 sec swells continue, with winds turning slightly more easterly, generating a Moderate Risk for rip currents for areas from Edisto, SC to Altamaha Sound, GA.

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.