Hurricane Michael is on track to make landfall in Florida’s Panhandle Wednesday as one of the fiercest storms the region has ever seen. While Florence drenched the Carolinas with record rainfall and other hurricanes attack with wind, Michael’s main threat will be surge.
The National Hurricane Center is forecasting Michael could send up to 13 feet of storm surge roaring ashore. That’s a lot of water, and there are a handful of interwoven factors explaining why the surge could be so high.
First, there’s the storm itself. Michael is a pretty big. Hurricane-force winds extend 35 miles out from the now Category 3 storm’s core, but tropical storm-force winds extend a whopping 185 miles outward. As the storm rotates, its long, windy arms scoop up water and push it along.
The underwater and shoreline topography of the Gulf Coast will lend a hand. The area Michael is headed has a shallow continental shelf that extends up to 90 miles offshore. That water is a lot easier to stir up than the deep ocean.
“Apalachee Bay very efficiently generates storm surge because of its concave shape and shallow bathymetry, or water depth,” Hal Needham, a storm surge expert and founder of Marine Weather and Climate, told Earther. Apalachee Bay sits smack between Cedar Key and Indian Pass, right at the epicenter of the highest surge forecasts.
Needham also warned of a terrifying-sounding “shelf wave” as Michael pushes north. Because the storm’s movement mirrors the Florida coastline, it basically traps a wave that “travels along the coast in the same direction as the storm” according to Needham. This happened during Hurricane Dennis, the last major hurricane to hit the Panhandle in 2005, and contributed to higher surge.
The pile on doesn’t stop there, though. Michael’s arrival coincides with the king tides, an annual tradition of the highest tides of the year in Florida which occur when the moon is full or new and the Earth is closest to the Sun. The storm is expected to make landfall sometime in the late morning or early afternoon. Thankfully the high tide isn’t until around 10 p.m., but Michael will still strike when the tide is rising.
And complete the whole shit show scenario, there’s sea level rise. Carbon pollution has contributed to melting land ice and warming and expanding the ocean. Florida’s Gulf Coast has seen sea level rise 8-9 inches over the past century. Sea level rise has ushered in a sunny day flooding crisis across the U.S., and it’s giving storms like Michael a boost they don’t really need.
Update 5:07 p.m. ET: This post has been updated to reflect the 5 p.m. update from the National Hurricane Center, which upgraded Michael to Category 3 storm with 13 feet of surge potential.