textproduct: Charleston

WHAT HAS CHANGED

Updated the Marine section to address the waterspout potential this morning. In addition, the Aviation section was updated for the 12Z TAFs.

KEY MESSAGES

- 1) There is the potential for localized excessive rainfall today across the forecast area, especially along the coastal counties this morning.

- 2) The typical summertime pattern will continue this weekend into next week. The threat for isolated strong to severe thunderstorms and localized heavy rainfall will exist each day, with heat concerns returning for those along the coast.

- 3) Minor coastal flooding possible along the South Carolina coast with evening high tide cycles next week.

DISCUSSION

KEY MESSAGE 1: There is the potential for localized excessive rainfall today across the forecast area, especially along the coastal counties this morning.

Sfc high pressure will remain centered near Bermuda today. Near term guidance indicates that a inverted trough will rotate on the west side of the high, pushing onshore along the GA/SC coast this morning. Recent runs of the HRRR, HREF, and RRFS indicate that showers and embedded thunderstorms will increase in coverage as the trough crosses the Gulf Stream this morning. The convection will push west, reaching onshore across the Savannah River during the pre- dawn hours. Coverage of convection may increase along the SC coast during the daylight morning hours. These showers and thunderstorms should develop within an environment featuring PW values between 2- 2.3" and MLCAPE of 1000-1500 J/kg. The combination of deep moisture and adequate instability may lead to areas of heavy rainfall over the coastal counties. HREF probability of 1"/3hr peaks around 80% near Savannah, with broad 30% across the coastal counties for 3"/3hrs. WPC has highlighted the area with a slight risk for excessive rainfall for today. Given the HREF rainfall probabilities, some coastal areas between Liberty to coastal Colleton, may see totals exceed 3". If the rainfall occurs over one of the coastal cities, including Savannah, Beaufort, and Charleston, then Flood Advisories or Flash Flood Warnings could be needed.

KEY MESSAGE 2: The typical summertime pattern will continue this weekend into next week. The threat for isolated strong to severe thunderstorms and localized heavy rainfall will exist each day, with heat concerns returning for those along the coast.

As the pattern with deep high pressure over the western Atlantic and Eastern Seaboard continues, daily scattered convection chances will remain possible. While most of this activity will be diurnally driven by the afternoon sea-breeze, scattered morning showers and thunderstorms can't be ruled out but will be dependent on how the overnight convection progresses. PWATs are expected to remain in the 1.75-2.0 inch range, and given slow storm motions locally heavy rainfall will be possible each day into the middle of the week. While 1500-2500 J/kg of CAPE will develop by the afternoon hours, the weak flow aloft will result in 0-6 km bulk shear values remaining near 10 knots, suggesting pulse-like storms rather than organized convection. Given the high water loading potential and ~500 J/kg of DCAPE, strong wind gusts would be the primary risk with any stronger thunderstorms. As a weak trough begins to enter our western areas Wednesday, surface flow becomes a bit more westerly which should keep the sea breeze pinned closer to the coast, limiting spatial coverage of showers and thunderstorms.

As for temperatures, Sunday and Monday will likely see high temperatures in the lower to mid 90s, with mid 90s looking to become more widespread by Tuesday and continuing into the end of the week as the aforementioned trough slowly shifts eastwards. Inland areas will likely see enough surface mixing to limit dew points to the mid 70s, while those along the coast will likely see dew points linger in the upper 70s to lower 80s. Combined with temperatures in the mid 90s, will likely see some heat index values in the 105-110 range along the coast on Monday, with similar heat index values Tuesday through Thursday.

KEY MESSAGE 3: Minor coastal flooding possible along the South Carolina coast with evening high tide cycles next week.

Perigean new moon will bring elevated tidal ranges next week. Even modest tidal departures during the evening high tide cycles Monday through Thursday would bring tidal levels approaching or exceeding minor coastal flooding thresholds, though the forecast currently has south-southwesterly winds next week which would keep tidal departures low. Continue to monitor forecast updates through the weekend as the total water level forecast gets refined.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

12Z TAFs: A coastal trough will drift onshore along the GA/SC coast this morning. This trough should result in rounds of showers and thunderstorms across the terminals this morning, highlighted with TEMPOs from 12-17Z. Once the trough passes, winds will turn from the SSE and increase to around 10 kts, with convection pushing inland on an early sea breeze. The mid to late afternoon hours should see decreasing PoPs for convection. However, KJZI could see showers with a VCTS into the mid afternoon. This evening is expected to feature decreasing winds and dry conditions.

Extended Aviation Outlook: Periodic flight restrictions are expected in showers and thunderstorms through early next week.

MARINE

This morning: Conditions will once again be favorable for the development of waterspouts across the nearshore and offshore waters of Southeast South Carolina and Southeast Georgia, including the Charleston Harbor, this morning. The waterspout risk will be highest near lines of towering clouds and in the vicinity of showers and thunderstorms. Conditions will become less favorable for waterspout development by late this morning as the sea breeze begins to form along the beaches.

Today: Sfc high pressure will remain centered near Bermuda today. Near term guidance indicates that a inverted trough will rotate on the west side of the high, pushing onshore along the GA/SC coast this morning. This feature should support numerous showers and thunderstorms across the marine zones today. Some storms may produce localized wind gusts in excess of 34 kts this morning. Otherwise, the pattern will support southeast wind around 10 kts and wave heights between 3 to 4 ft.

Sunday through Wednesday: Atlantic high pressure will be the dominant synoptic feature Sunday into next week. Light to moderate winds prevail on Sunday and Monday, though gusty winds are expected along the land/sea interface each afternoon associated with the sea breeze. Nocturnal jetting looks to remain possible Monday night through Thursday night as a weak surface trough moves eastwards over land, with the persistent strong high pressure offshore and very warm waters. Small Craft Advisories currently look unlikely, but something to monitor.

CHS WATCHES/WARNINGS/ADVISORIES

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