textproduct: Charleston

WHAT HAS CHANGED

The Aviation section was updated for the 0Z TAFs.

KEY MESSAGES

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

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

DISCUSSION

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

A wedge of high pressure will strengthen across the Carolinas and Georgia Wednesday, likely forcing a cold front across far southern zones early-mid morning, then south of the Altamaha River before noon. The position of the front and strengthening wedge will play the largest role in precip coverage locally, limiting the risk to a few rain showers only across inland and northern areas. Best chances for precip should be along the I-95 corridor in Southeast Georgia, where warmest temps prevail early. Scattered showers along with a few thunderstorms are possible in this area, but the threat for a stronger thunderstorm has lowered based on an earlier time of fropa.

Cold air advection and a tightening pressure gradient associated with the nearby wedge will likely support breezy conditions Wednesday afternoon and Thursday. Northerly winds could gust upwards to 20-25 mph Wednesday afternoon/night, then up to 25-35 mph Thursday, strongest near coastal areas. Conditions appear to fall just short of Wind Advisory criteria over land, but could warrant a Lake Wind Advisory across Lake Moultrie, especially Thursday. Temperatures will be noticeably cooler than previous days post fropa, with highs only reaching the mid-upper 70s Thursday and Friday, prior to gradually warming into the 80s this weekend. Overnight lows should also dip into the low-mid 50s across the interior late week.

KEY MESSAGE 2: The threat for coastal flooding will increase mid to late week.

As a full moon approaches on 9/26, breezy northeast winds develop Wednesday and linger into Friday, which may result in coastal flooding issues as tidal departures rise. Will likely see minor coastal flooding Wednesday evening along the Charleston and Colleton county coast, and again on Thursday evening. Latest guidance would indicate even the Friday morning high tide may see minor coastal flooding, with another round expected for the evening high tide. Thursday evening and Friday evening both have potential for reaching moderate flood stage in the Charleston Harbor.

Impacts are less clear moving down the rest of the southeast South Carolina coast and into southeast Georgia, with the latest guidance keeping water levels below minor flood stage at Fort Pulaski. The two high tides where minor flood stage cannot entirely be ruled out yet are Thursday and Friday evening.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Prior to the 0Z TAFs, KCLX detected several showers and isolated thunderstorms near the terminals. Each TAF will highlight VCSH through 3Z this evening. A wedged high is forecast to build across the region tonight, resulting in strengthening NE winds and lowering ceilings. MOS and forecast soundings indicate a round of MVFR ceilings may develop during the pre-dawn hours and persist until the early afternoon. Once mixing deepens in the morning, northeast winds are forecast to develop gusts around 20 kts.

Extended Aviation Outlook: VFR conditions should prevail at all terminals late this week.

MARINE

Through Tonight: Marginally breezy northeast winds this afternoon will remain at similar strength into the overnight hours, with periodic showers and thunderstorms capable of gusty winds and frequent lightning.

Wednesday-Friday: A cold front will be pushing through during the morning hours on Wednesday, with a strong surge in northeasterly flow as the pinched pressure gradient (aka the wedge) settles in. Breezy winds ramp up during the morning hours, with wind gusts of 25 to 34 knots remaining across the local waters into Friday afternoon. There is a 30-55% chance for Gales for areas 20+nm off the coast, with the trend being increasing probabilities for a larger spatial area. Given the breezy winds, a Small Craft Advisory is in effect for all near-shore zones, as well as the zone from Savannah to the Altamaha River, GA from 20-60nm out. A Gale Watch from Thursday evening into Friday was considered, but would like to see more data before committing to that. In addition, wave heights of 5-8 ft will likely accompany the breezy winds for areas 10+ nm away from the coast Thursday morning through Friday evening before winds begin to weaken.

Saturday-Sunday: The wedge continues to weaken, further decreasing the wind strength throughout the day. Seas will remain unsettled, with offshore zones (20+nm offshore) seeing 6ft+ waves continuing into the evening hours before decreasing below 6 ft.

Rip Currents: There is a Moderate risk for rip currents along GA beaches Wednesday as northerly winds and increasing swell occurs behind a cold front. On Thursday, a strong coastal low strengthens well offshore of Virginia, favoring a continuation of breezy winds, building wave heights and 5-6 ft swells with near 8 second periods along the coast. This setup will further increase the risk for rip currents along the entire SC/GA coast, and should result in a high rip current risk at all area beaches Thursday.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory from 5 AM Wednesday to 5 PM EDT Friday for AMZ360-362. Small Craft Advisory from 8 AM Wednesday to 11 PM EDT Friday for AMZ364. Small Craft Advisory from 8 AM Wednesday to 8 AM EDT Sunday for AMZ384.