Hurricane Idalia is expected to come ashore Wednesday as a Category 3 storm, bringing a storm surge of 10-15 feet to the Big Bend of Florida.
Wednesday also marks a full moon. While these two events would seem unrelated, the storm surge from a landfalling hurricane could be made worse by a full moon.
Full and new moons cause what are known as "spring tides," which essentially make for higher high tides and lower low tides. In between the full and new moon cycles are quarter moons. At these times, the high tides aren't as high, and the low tides aren't as low.
"During full or new moons — which occur when the Earth, sun, and moon are nearly in alignment — average tidal ranges are slightly larger," the National Oceanic and Atmospheric Administration said. "This occurs twice each month. The moon appears new (dark) when it is directly between the Earth and the sun. The moon appears full when the Earth is between the moon and the sun. In both cases, the gravitational pull of the sun is 'added' to the gravitational pull of the moon on Earth, causing the oceans to bulge a bit more than usual. This means that high tides are a little higher and low tides are a little lower than average."
Hurricane Idalia's landfall is expected Wednesday morning.
For a spot like Cedar Key, Florida, spring tides can add about a foot to the high tide cycle. NOAA estimates that Cedar Key will experience a high tide at 1:45 p.m. ET on Wednesday that reaches 4.7 feet. A week ago, the area had a high tide that was about 3.7 feet, according to NOAA data.
At Clearwater Beach, the high tide is expected to reach about 3.7 feet, which is about a foot higher than a week ago during high tide around 1:45 p.m.
The effect can be even higher on Florida's east coast. Jacksonville Beach is expecting a high tide of 6.5 feet in the evening, which can be about 1.5 feet higher than normal high tide levels.
The National Hurricane Center says areas from Aucilla River to Yankeetown could have 10 to 15 feet of water rise if the hurricane hits Florida at high tide.
The morning low tide for Cedar Key is expected to reach 1.5 feet, meaning the storm surge could be nearly 3 feet lower if the hurricane comes ashore around 7:50 a.m.
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