A rare blue supermoon could raise tides above normal just as Hurricane Idalia smashes its way across Florida’s west coast, exacerbating flooding from the storm.
The moon will be closest to the Earth on Wednesday, the day Idalia made landfall in Florida. While a supermoon can make for a spectacular backdrop in photos of landmarks around the world, its intensified gravitational pull also makes tides higher.
“I would say the timing is pretty bad for this one,” said Brian Haines, the meteorologist in charge at the National Weather Service office in Charleston, South Carolina.
It is expected to make tidal flooding worse not only in Florida, but in states such as Georgia and South Carolina, where Haines’s office has been warning residents that parts of Charleston could be under water by Wednesday night.
When the moon is full, the sun and the moon are pulling in the same direction, which has the effect of increasing tides above normal ranges, said Kerry Emanuel, professor emeritus of atmospheric science at the Massachusetts Institute of Technology.
The moon’s gravitational pulls are even stronger when it is closer to Earth, so the tides are even higher.
The storm surge is often the greatest killer when hurricanes strike. “There’s a saying that you hide from the wind and run from the water, and hopefully people are heeding that advice,” said Brian Tang, associate professor of atmospheric science at University at Albany in New York.
The part of north-west Florida that has been hit by Idalia is especially vulnerable to storm surge because of the region’s geography. The continental shelf extends so far out from the coast and has a gradual slope, allowing the ocean to grow higher as hurricane winds drive the water on to land, Tang said.
The shape of the coast in that region – known as Florida’s Big Bend area, where the northern part of the state’s peninsula meets the panhandle – is also curved inward, which can focus the storm surge to make it even more dangerous, he said.