New moon could worsen storm surge from Florence

There is no good time for a hurricane to threaten the North Carolina coast, but next week would be better, tidally speaking.

Winds get much of the attention in the days and hours leading up to the moment a hurricane makes landfall, but it is flooding, especially storm surge, that leaves the most damage behind. Sunday morning’s new moon could make that storm surge worse.

Tides occur as the moon’s gravity pulls on the oceans. Centrifugal force creates a similar bulge of water on the opposite side of the Earth. These sloshy bulges align with the moon while the Earth rotates beneath, creating two high and two low tides each day.

During the new phase, the pull is intensified by the sun’s gravity as the Earth, moon and sun line up.  These spring or king tides result in about 20% higher tides.  Tidal predictions are slightly higher through mid-week, in part because the moon is near perigee, the closest point in its orbit. The effect perigee has on high tide isn’t as great as the new moon, but each extra inch can increase flooding.

Ultimately, any storm surge is determined by a hurricane’s strength, speed, and track as well as the shape of the coastline and underwater terrain. The tide charts all along the Carolina coast tell us that, should Florence bring a storm surge, later in the week would be better.