textproduct: Charleston

WHAT HAS CHANGED

The Aviation section has been updated for the 00z TAF issuance.

KEY MESSAGES

- 1) The coastal flood risk will linger through the end of this week.

- 2) Warm and dry conditions will extend through most of the week.

- 3) Unsettled weather will return late week into the weekend with fall-like conditions early next week.

DISCUSSION

KEY MESSAGE 1: The coastal flood risk will linger through the end of this week.

As the nor'easter travels further up the Eastern Seaboard, coastal flooding will still pose a risk through the end of the week (esp. for the Charleston Harbor). It's possible that the lingering conditions could be from the build up of tidal waters across the inland waterways and/or the movement of the gulf stream has slowed.

Charleston Harbor: Tidal levels could reach 7.3 ft MLLW in the Charleston Harbor for tomorrow morning's high tide (~11AM). Therefore, a Coastal Flood Advisory will likely be issued for tomorrow morning's high tide for Charleston and Colleton Counties. Saltwater inundation will be possible 2 to 3 hours before and after high tide, and will likely result in some roads becoming impassable.

Thereafter, minor coastal flooding conditions could continue through the end of the week for the Charleston Harbor.

Fort Pulaski: Tidal levels could reach 9.2 ft MLLW for tomorrow morning's high tide in Fort Pulaski (~11AM), thus this will not warrant a Coastal Flood Advisory for lower South Carolina and southeast Georgia.

KEY MESSAGE 2: Warm and dry conditions will extend through most of the week.

Ridging aloft will build into the southeastern states through the week, yielding a rain-free pattern through Thursday. High temperatures will climb into the mid to upper 80s daily, roughly 5 degrees above normal for late Sept/early Oct, with parts of Southeast Georgia reaching the lower 90s. Lows will gradually warm each night, hovering in the mid to upper 60s inland and low to mid 70s near the beaches.

KEY MESSAGE 3: Unsettled weather will return late week into the weekend with fall-like conditions early next week.

Net moisture levels will begin to steadily increase Friday and persist into the weekend as a modest return flow sets up along the backside of subtropical high pressure centered well offshore. A cold front will approach Saturday then cross the area Sunday before settling over Florida Monday into Tuesday as high pressure wedges south across the Carolinas and Georgia. PWATs are forecast to surge as high as 2.25-2.50" ahead of the front which will run ~2 standard deviations above climatology for early October. Weak forcing aloft is noted in model cross- sections owing to subtle DCVA ahead of a weak, mostly sheared southern stream shortwave. So, Despite the presence of a high net moisture values, there is much uncertainty with regards to how much rainfall and resulting QPF will occur given this weak forcing pattern. This is reflected in the latest guidance showing a fairly large interquartile range (IQR) in the various QPF forecasts across the entire set of GFS and ECMWF ensemble members. Pops for the Saturday into Monday time periods were limited to the likely range for now given this uncertainty. Another strong cold air damming (CAD) event is expected to setup for early next week with a return to cooler, fall-like conditions becoming increasingly likely along with breezy to windy conditions possible, especially at the coast.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

VFR conditions are expected to prevail at KCHS, KJZI, and KSAV through 00z Thursday. The only real forecast issue is the potential for some shallow ground fog around sunrise, as well as the low end potential for low stratus to try and spread in from the west. For now we have kept the forecast VFR. KSAV likely has the best chance of seeing sub-VFR conditions, but current thinking is that the more notable fog and stratus concerns will remain inland.

Extended Aviation Outlook: There will be an elevated risk for sub-VFR conditions in showers and thunderstorms over the weekend.

MARINE

Through Tonight: Quiet marine conditions will prevail across the local waters with easterly winds 10 kt or less and seas less than 2 ft.

Wednesday through Friday: An east to southeast flow will prevail across the coastal waters through Friday as high pressure is forecast to remain to the east, well offshore. Local sea breeze enhancements look likely each afternoon near the land/sea interface and Charleston Harbor, but no meaningful impacts are expected. Wind speeds will generally remain 10 kt or less (except 10-15 kt within the sea breeze circulation each afternoon) with seas 3 ft or less.

Rip Currents: A Moderate Risk of rip currents is in place for all southeast South Carolina and southeast Georgia beaches Wednesday due to 13 second swell moving in.

CHS WATCHES/WARNINGS/ADVISORIES

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