Hilton Head Island, SC Weather

What Has Changed

Aviation updated to represent the 12Z aviation forecast.

Key Messages

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

- 2) 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.

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

Discussion

KEY MESSAGE 1: 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 remainder of 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.

Sunday Morning: Tide levels at the Charleston Harbor are forecast to reach 7.9-8.1 ft MLLW, resulting in a Coastal Flood Warning for Charleston and coastal Colleton. In addition, at these tide levels, up to half a foot of saltwater inundation will be possible for tidal Berkeley county, resulting in a Coastal Flood Advisory. Lastly, a Coastal Flood Advisory has been issued for Fort Pulaski as well, from Beaufort County in SC to McIntosh County in GA, with forecast values of 10.0-10.2 ft MLLW. Current departures are running a little behind forecast; however, winds offshore are expected to increase throughout the morning as we approach high tide and much like yesterday morning we should see things quickly increase through the morning.

Sunday Evening: Tide levels at the Charleston Harbor are forecast to reach 7.4-7.6 ft MLLW, whereas at Fort Pulaski the tide is expected to reach 9.6-9.8 ft MLLW. Coastal flood advisories will most likely be needed.

Next Week: 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. The one thing keeping us from considering major flooding at Fort Pulaski outside of climatology is that the winds offshore should relax some heading into early next week. While astronomical tides will be running high, the relaxed wind field will likely not support as high departures and without any other considerations for increased departures such as rainfall, there is not enough support for us to feel we can push past the climatological normal. Nonetheless, 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.

KEY MESSAGE 2: Strong northeast flow will result in several hazards including gusty lake winds, rip currents, high surf, and beach erosion.

Aviation

Northeasterly winds will slowly increase after sunrise. Areas well away from the coast are expected to see gusts of 20-25 knots, while those along the coast will be closer to 30 knots.

Extended Aviation Outlook: Breezy north-northeast winds are expected at KCHS/KJZI/KSAV daily through the week. There are no other high confidence concerns.