textproduct: Charleston

WHAT HAS CHANGED

All Key Messages and sections were updated.

KEY MESSAGES

- 1) Breezy and cooler weather will persist into the weekend.

- 2) The coastal flood risk ramps up due to persistent northeast winds and high astronomical tides.

- 3) High Risk for dangerous rip currents today due to strong offshore swell, with an elevated risk continuing through the weekend.

DISCUSSION

KEY MESSAGE 1: Breezy and cooler weather will persist into the weekend.

Thursday: Rather impressive cold air damming (CAD) for early Fall has developed a firm grip on the sensible weather the next 24 hours with today being the peak of the wedge. Looking a loft, the parent upper trough will begin to eject over the Mid- Atlantic this morning and into the afternoon. Strong surface cyclogenesis has begun off the Carolina coast as the beginnings of a stout early season nor-easter begins. The surface pressure gradient is expected to tighten throughout the day today as the surface low strengthens. Surface north-easterlies shall increase with frequent gusts across the area around 25 to 30 mph especially along the coast. While this is not enough to warrant any wind products, conditions could be a little treacherous across area bridges this afternoon and caution is advised. Along with the breezy coniditons, the upper trough moving overhead will support light isentropic upglide over top the cold wedge. This typically results in widespread cloud cover and usually light drizzle/precipitation as warm moist air rises overtop the colder air and cools. Given cooler air within the wedge is firmly in place, plus the combination of poor solar insolation and some diabatic cooling with precip the expectations are for high temperatures to be stuck on the cooler side this afternoon. This is certainly a welcome change from brutal heat that the region has experienced for most of the summer. As is typical for CAD events, blended guidance has struggled with high temperatures and typically underdoes the isentropic ascent. As a result, we went rather aggressive in keeping temperatures on the cooler side of guidance with highs inland likely barely reaching 70 degrees and low 70s along most of the coast. Depending on how much drizzle occurs; this may not be enough and much like yesterday high temperatures could even struggle to get into the upper 60s for most of the area. So if you're planning to head out do not expect the warm side.

Friday into Sunday: By Friday, the upper trough and adjacent nor-easter shall lift off into the northeast and towards the northern Atlantic eroding the wedge in the process. While the wedge may be gone, the cold air will not be as stiff northerly winds behind the trough shall usher in a rather stout punch of continental polar air. Conditions should dry out rather quickly on Friday and Saturday with clouds clearing and temperatures dropping. Highs on Friday and Saturday will be warmer given the drier column and plenty of sunshine to support heating but overnight lows will be noticeably cooler with temperatures in the 50s except for the immediate coastline. This will be our first real shot of Fall!

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

Breezy northeasterly flow combined with the upcoming full moon (9/26) will yield an increase in tidal departures across the region. Coastal flooding impacts will ramp up today as each of the next three consecutive high tides starting this evening (Thursday evening, Friday morning, and Friday evening) has the potential to reach moderate flood stage along the Charleston and Colleton County coastlines. Coastal Flood Advisories will likely be needed during each high tide cycle. An extended period of coastal flooding impacts could be seen during each high tide cycle through early next week.

Further south along the lower South Carolina and southeast Georgia coasts, this evening's high tide has the potential to reach minor flood stage (around 9.5 ft MLLW). A Coastal Flood Advisory could be needed. Additionally, latest guidance continues to target peaks near the minor flood threshold for the Friday morning and evening high tides.

KEY MESSAGE 3: High Risk for dangerous rip currents today due to strong offshore swell, with an elevated risk continuing through the weekend.

Strengthening low pressure well off the Carolina coast will support breezy winds, building surf, and 7-8 second swells today. This setup will drive a High Risk for rip currents along the entire South Carolina and Georgia coastline. On Friday, the surf will transition to a longer-period swell (12 seconds at 3-4 ft), resulting in a Moderate Risk for all area beaches. An elevated rip current risk will persist into the weekend as long-period swell lingers.

AVIATION /12Z THURSDAY THROUGH MONDAY/

12Z TAFs: MVFR conditions should prevail at all tafs sites through this afternoon. Stiff northerly winds will also persist around 10 to 15 knots with gusts up to 25 knots. Scattered showers and light drizzle should develop during the afternoon with the best chances of showers across CHS and JZI. Ceilings should gradually lift into the evening. VFR condition should return overnight as skies clear. Northerly winds will remain elevated overnight.

Extended Aviation Outlook: Gusty winds will persist into Thursday, possibly Friday.

MARINE

Thursday: Strong northeasterly flow will persist throughout the day today with likely Gale conditions beginning over the offshore waters this morning. Winds across all the marine zones will range from around 20 knots nearshore to 25 to 30 knots well offshore with gusts well offshore nearing 40 knots. Seas will quickly increase to around 5 to 9 feet nearshore and 9 to 11 feet well offshore. These conditions are expected to continue through Thursday night.

Friday and Saturday: Winds and seas will gradually subside Friday into Saturday as the inland wedge weakens and the offshore low moves northeast away from the area. Northerly wind gusts are expected to drop below 25 kt on Friday, though seas will be slower to diminish. Small Craft Advisories will likely be needed through Saturday night, mainly for 6 ft seas lingering across the outer Georgia waters.

Sunday through Tuesday: Marine conditions will continue to improve Sunday as the pressure gradient weakens under broad surface high pressure. No headlines are anticipated, with southerly winds 10 kt or less and seas subsiding to 2-3 ft.

CHS WATCHES/WARNINGS/ADVISORIES

GA...High Risk for Rip Currents through this evening for GAZ217-219-239- 241. SC...High Risk for Rip Currents through this evening for SCZ148>151. MARINE...Small Craft Advisory until 11 PM EDT this evening for AMZ340. Small Craft Advisory until 8 PM EDT Friday for AMZ360-362. Small Craft Advisory until 8 AM EDT Saturday for AMZ364. Gale Warning until 6 AM EDT Friday for AMZ380-382. Small Craft Advisory until 2 PM EDT this afternoon for AMZ384. Gale Warning from 2 PM this afternoon to 6 AM EDT Friday for AMZ384.