textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated and a new key message was added.

KEY MESSAGES

- 1) Breezy and cooler weather arrives behind a cold front today and Thursday.

- 2) The threat for coastal flooding will increase mid to late week.

- 3) High risk of dangerous rip currents Thursday across all South Carolina and Georgia beaches.

DISCUSSION

KEY MESSAGE 1: Breezy and cooler weather arrives behind a cold front today and Thursday.

Surface high pressure will build over the area as cold air damming has begun across the Carolinas. The wedge boundary has pushed through the area this morning and will continue to spill southward as strong northerly winds help re-enforce the cold air over the next 24 hours. As the surface gradient tightens the winds should increase leading to stronger cold advection through the area. Given the combination of moist midlevels and strengthening wedge; increased cloud cover is expected through most of the day today with a few isolated showers along the coast. The lack of solar insolation due to the cloud cover should assist in locking the CAD in place and keeping highs in low 80s to upper 70s across most of the area. The forecast highs for today have been lowered a few degrees and this could be conservative depending on how quickly the cold air moves in.

By Thursday the wedge will be firmly in place as cloud cover and strong northeasterly winds continue to pump cooler air into the area. Highs on Thursday will struggle to reach the mid 70s across most of the area. At this time a rather potent upper trough and adjacent surface low will strengthen over the Mid- Atlantic and off the coast of North Carolina/Virginia. The quickly strengthening gradient between the surface low off the coast and high pressure over the lands will support rather gusty winds across the area Thursday afternoon. Wind gusts in the 25 to 30 mph range will be possible during the afternoon on Thursday and depending on where the surface low tracks/develops some higher gusts along the coast cannot be ruled out. Wind should relax by Friday and into the weekend as the low lifts northeast into the Atlantic and drier and cooler air moves into the area over the weekend.

KEY MESSAGE 2: The coastal flood risk ramps up through Friday due to persistent northeast winds and high astronomical tides.

An approaching full moon (9/26), combined with persistent, breezy northeast winds, will drive up tidal departures across the region.

Charleston and Colleton county coasts: Minor coastal flooding is likely during the evening high tide today, with flooding concerns ramping up Thursday into Friday. The Thursday evening and Friday evening high tides pose the highest threat, with potential to reach moderate flood stage along the Charleston and Colleton county coasts. Additionally, guidance indicates the Friday morning high tide could see minor coastal flooding.

Lower South Carolina and Southeast Georgia Coasts: Impacts are less clear further south, with latest guidance keeping water levels just below minor flood stage at Fort Pulaski. However, the Thursday evening and Friday evening high tides remain the two time frames where minor flooding cannot be entirely ruled out.

KEY MESSAGE 3: High risk of dangerous rip currents Thursday across all South Carolina and Georgia beaches.

Northeasterly winds and increasing swell in the wake of a cold front will produce a Moderate Risk for rip currents along the Charleston County and southeast Georgia beaches today.

On Thursday, a strong coastal low strengthening well offshore of Virginia will maintain breezy winds, building wave heights, and large swells with a 7-8 second period along the coast. This setup will drive a High Risk for rip currents along the entire South Carolina and Georgia coastline on Thursday.

An elevated risk for rip currents will persist into the weekend due to incoming longer period (10-12 second) swell.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

IFR MVFR ceilings will continue over the area with IFR mainly near KSAV. Winds will remain out of the north and increase to around 10 to 15 knots with gusts up to 20 knots. Ceilings should lift to MVFR at all sites this afternoon before dropping to low end MVFR to IFR once again after midnight tonight.

Extended Aviation Outlook: Gusty north to northeast winds will impact all terminals Thursday. Northeasterly gusts of 20-25 kt are expected, with localized gusts up to 30 kt possible across the Charleston Tri-County area (primarily affecting KCHS and/or KJZI).

MARINE

Through Wednesday night: Northeasterly winds will continue to strengthen throughout the day and into the overnight hours as advisory criteria should be met for all area waters excluding Charleston Harbor by this afternoon. Winds and seas should continue to slowly climb throughout the overnight as the surface gradient continues to tighten.

Thursday through Monday: An inland wedge interacting with a deepening low off the North Carolina coast will produce a tight pressure gradient across the waters. As a result, winds will peak Thursday evening. A Gale Watch has been issued for the outer South Carolina and Georgia waters (from 20-60 nm), though the nearshore waters could briefly approach gale force as well. Seas will peak Thursday night between 5-9 ft across the nearshore waters (out to 20 nm) and 9-11 ft across the outer waters. Winds and seas will gradually subside Friday into Saturday as the gradient relaxes. However, Small Craft Advisories could be needed through at least Saturday night, with 6 ft seas potentially lingering across the outer Georgia waters into Sunday morning.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory until 5 PM EDT Friday for AMZ360-362. Small Craft Advisory until 11 PM EDT Friday for AMZ364. Gale Watch from Thursday afternoon through Friday morning for AMZ380-382-384. Small Craft Advisory until 2 PM EDT Thursday for AMZ384.