textproduct: Charleston

WHAT HAS CHANGED

The aviation section updated for the 12Z TAFs.

KEY MESSAGES

- 1) A Flood Watch is in effect for the Charleston Quad-County in the SC Lowcountry. Locally heavy rainfall will be possible today and Saturday.

DISCUSSION

KEY MESSAGE 1: A Flood Watch is in effect for the Charleston Quad-County in the SC Lowcountry. Locally heavy rainfall will be possible today and Saturday.

Today: A slow moving front will drift southward today into southeastern SC. The afternoon sea breeze is forecast to begin pushing inland around noontime, interacting with the front beginning in the early afternoon. The interaction of the slow moving (nearly stalled) front and the sea breeze will lead to a threat of heavy rainfall this afternoon across the SC Lowcountry and Southeastern GA. A Flood Watch has been issued for the Charleston Quad-County, where the greatest risk of heavy rainfall resides. Forecast soundings show long, skinny CAPE profiles with CAPE values around 1500-2000 J/kg and Corfidi vectors are forecast to only be around 5 to 10 knots. These parameters support heavy rainfall across the watch area. Additionally, PWAT values are forecast to reach upwards of 2.4", which would exceed the daily max according to SPC Climatology. The 00Z HREF probabilities also support the heavy rainfall threat, with a 50% contour of the 3-hr QPF exceeding 3" across the watch area. Locations within the watch will likely see 3-5 inches, with 1-3 inches elsewhere. With the convective nature of the precipitation it cannot be ruled out that some locations could see slightly higher amounts. The main timeframe for these heavy downpours is 3-9 PM.

Saturday: Our aforementioned front will have moved well into the area by the morning hours Saturday with a large slug of moisture streaming up from the Gulf coast. The main trough axis looks to have moved slightly eastward and will continue to slowly lift east- northeast throughout the day as a series of subtle shortwaves moves through the broader west-southwesterly flow a loft. Saturday is looking very similar to Friday; however, with the slight shift in the trough axis the best forcing will be more focused along the coastline. Showers and storms will likely already be ongoing early in the morning mainly north of I-26 but the real show likely arrives during the afternoon. Much like Friday storms will likely quickly develop during the afternoon along the seabreeze. The only main difference is with the main trough axis closer to the coast, storms may be more confined along the immediate coastline rather than inland. Given this uncertainty of location being over maybe more marshy sandy soils that can handle more water than say inland or urban areas, we have withheld any flash flood watch for this time. However, PWATS in place will range in the 2.2 to 2.4 inch range which would rival the daily record PWAT at CHS and right at our average max PWAT for this time of year. In-short this airmass will be rather juicy and capable of rather intense rainfall rates likely in the 2 to 3 inches per hour range. IF, storms are able to develop more closer to the Charleston metro or further inland on Saturday then flash flooding concerns would quickly escalate. On top of this, we will have to see how Friday plays out and how much rain falls then which could further increase the flash flood potential Saturday as soils become saturated. Depending on trends, we will likely make a decision on a continuation of the Flash Flood watch by later today or tonight. The area of greatest concerns is certainly centered around the quad-county area and Charleston Metro.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

12Z TAFs: Conditions across the terminals will remain dry with light SW winds through early this morning. Scattered to numerous showers and thunderstorms will likely develop along the sea breeze across KCHS and KJZI between 18-22Z. These storms will tap into moderate instability and very deep moisture, creating torrential downpours. Conditions during thunderstorms could rapidly become restrictive. The TAFs will highlight the potential for thunderstorms with TEMPOs from 18-20Z at KCHS and KJZI, one hour later at KSAV. Showers could linger into the overnight hours, however confidence is very low regarding any potential impacts at the terminals.

Extended Aviation Outlook: A weak front nearby will continue to provide periods of flight restrictions within any showers and thunderstorms that develop through Saturday.

MARINE

Today through Wednesday: Southwesterly to southerly flow will persist through Saturday as a weak front moves into the marine waters from the north. Winds will temporarily become northerly behind the front Saturday night into Sunday before returning to a light southwesterly flow by the beginning of next week.

Rip Currents: There is a Moderate Risk for rip currents for all local beaches today (Friday) due to longer period swell around 8 seconds and enhanced southwesterly wind gusts.

CLIMATE

Record High Temperatures:

July 29: KCHS: 100/1993 KCXM: 99/1999

Record High Minimum Temperatures:

July 23: KCHS: 80/1991 KCXM: 83/1952

July 24: KCHS: 81/2024

July 25: KCHS: 80/2011 KCXM: 82/2016 KSAV: 80/1893

July 26: KCHS: 78/2025 KSAV: 80/1884

July 28: KCHS: 80/2025

July 29: KCHS: 80/2016 KSAV: 82/1878

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...Flood Watch from noon EDT today through this evening for SCZ043>045-149-150-152. MARINE...None.