Charleston SC (CHS) — the National Weather Service forecast in plain English · Plaincast

What has changed

Updated aviation section to reflect the 12z aviation forecast.

Messages

1) Dry conditions and below normal temperatures will continue through early next week before gradually warming up by the end of the week.

2) A significant multi-day coastal flooding event is expected this weekend through at least the middle of next week.

3) Strong northeast flow this weekend and into early next week will result in several hazards including gusty lake winds, rip currents, high surf, and beach erosion.

Discussion

KEY MESSAGE 1: Dry conditions and below normal temperatures will continue through early next week before gradually warming up by the end of the week.

Today through Friday: The overall pattern will be rather persistent over the next 7 days or so with upper level ridging over the northern Gulf coast and a rather pesky upper trough/cutoff low meandering around the Bahamas. Surface high pressure has built down through the mid-atlantic with a weak wedge setting up across the Carolinas. Dry and cool conditions will prevail under the wedge through Sunday. The wedge should relax Monday into Tuesday as temperatures slowly climb back towards normal by midweek. By late in the week, the upper ridge should begin to breakdown and translate east across the southeastern US bringing a temporary warming to the area as highs climb back close to 80 degrees by Friday.

KEY MESSAGE 2: A significant multi-day coastal flooding event is expected this weekend through at least the middle of next week.

Astronomical tides will continue to rise through the weekend and into next week due to the upcoming full moon (10/26) and the lunar perigee (10/28). Large tidal departures are already ongoing, and with an extended period of strong northeast flow this weekend and into next week, these departures will increase in magnitude. The combination of the highest astronomical tides of the year and persistent strong northeast flow will result in a multi-day moderate to major coastal flooding event for the entire southeast GA/SC coast.

Upcoming morning high tide (~7 am): Moderate coastal flooding will likely occur at Charleston with the morning high tide cycle. The astronomical high tide is 6.19 ft MLLW and we are currently running a 1.3 ft departure as we head into the preceding low tide. We are expecting winds to increase offshore this morning leading to likely even higher departures occurring. We currently expect high tide to peak in the 7.5-7.6 ft MLLW range, and a Coastal Flood Advisory is in effect for Charleston and coastal Colleton counties. At Fort Pulaski, the astronomical high tide is expected to reach 8.05 ft MLLW and with the same expectations with departures we expect Fort Pulaski to reach 9.6 ft. A Coastal Flood ADvisory is in effect for all of the Georgia Coastline, coastal Beaufort and Coastal Jasper counties in South Carolina.

Over the weekend and into the middle of next week, there is increasing potential for multiple rounds of moderate to major coastal flooding at Charleston and minor to moderate coastal flooding at Fort Pulaski. The highest water levels are expected to occur with the Monday, Tuesday, and Wednesday morning high tide cycles. During these cycles, confidence is increasing that Charleston will exceed major flood stage (8.0 ft MLLW) and Fort Pulaski will exceed moderate flood stage (10.0 ft MLLW). There is even concern that Fort Pulaski could reach or exceed its major flood stage (10.5 ft MLLW), which has never happened in its history (records begin in 1935) outside of a tropical system. Coastal flooding will likely occur with both the morning and evening high cycles for several days, though the evening tide will be the lower of the two. Coastal Flood Advisories will definitely be needed, and Coastal Flood Watches/Warnings are very likely for some or all of the coast from Sunday through Wednesday.