The Science Behind Why Hurricane Milton Is So Powerful

By Jeffrey Kluger
October 8, 2024 2:35 PM EDT

Jane Castor, the mayor of Tampa, has little patience for local residents who plan to disobey the evacuation orders that have been issued in the run-up to Hurricane Milton’s expected landfall on Florida’s gulf coast on Wednesday evening, Oct. 9. “If you choose to stay in one of these evacuation areas,” she said in a CNN interview, “you’re going to die.”

Alarming? Yes. Hyperbole? Probably not. Milton is nothing short of a meteorological monster. The minimum threshold for a Category 5 storm—the most powerful type of hurricane—is sustained winds of 157 mph. Milton is exploding at 175 mph. Rainfall could reach a staggering 18 inches in parts of the Florida peninsula by Thursday and storm surges could reach 15 feet. What’s more, all of this happened fast.

A hurricane is said to undergo rapid intensification when its sustained winds increase by 35 mph in a 24-hour period. Milton blew through that benchmark, with wind speeds intensifying by 90 mph in 24 hours, from Sun. Oct 6, to Mon., Oct. 7, and 70 mph in just 13 hours within that window.

“Residents & visitors under evacuation warnings for #Milton need to leave NOW,” wrote FEMA administrator Deanne Criswell, on X. “This is a matter of life or death for people in Florida.”

Read more: The Superstorm Era Is Upon Us

How did Milton become such a beast—and does this portend more such storms to come? There have been a number of factors at play in the past few days and decades, all of them making their unfortunate contribution to an unfathomable storm.

A hurricane is a sort of atmospheric engine, spinning about its axis—counterclockwise north of the equator, clockwise south of the equator—thanks to the Coriolis effect, which is caused by the rotation of the earth. Like any engine, a hurricane requires fuel—typically in the form of heat and water in the atmosphere and ocean; and like any engine too, it produces exhaust—rain, wind, storm surges.

Much of the heat a hurricane needs to operate comes in the form of high surface temperatures in local bodies of water—in this case, the Gulf of Mexico. The minimum water temperature required to sustain a hurricane is 79°F, according to the National Ocean and Atmospheric Administration (NOAA). The temperature of Gulf waters off the coast of the city of Cancun, which is expected to feel Milton’s wrath as early as 7:00 p.m. tonight, Oct. 8, is 86°F. Off the coast of Tampa, the water readings are nearly as high, at 84°F.

Low wind shear matters too. Powerful shear in the upper atmosphere can effectively rip a hurricane apart by dispersing warm air above the eye and allowing cooler, less energetic air to flow in. There’s plenty of wind shear in the northern part of the Gulf of Mexico at the moment, but Milton is too far south to be much affected by it. When the storm does move to a more northerly location, the shear will start to have its way with it, but by that time Milton will have already collided with Florida.

The third powerful part of the environmental trifecta that is turbocharging the storm is high atmospheric humidity over the Gulf, which means a lot of airborne moisture. Humidity in the region is 62% today and is expected to rise to a sticky 68% by Wednesday. Relatively high air temperatures—exceeding 80°F—help the already soggy atmosphere entrain more water still, which it can dump down on communities in Milton’s path.

Read more: Here’s Where All The Strongest Hurricanes Have Hit the U.S. in the Past 50 Years

All of these are short-term meteorological factors, but long-term climatological ones are playing a role in the storm’s explosive growth too. The summer just past was the warmest on record in the northern hemisphere; August itself set a global record, closing out as the hottest month recorded in 175 years. That not only means more hurricanes, but ones playing out closer to shore, as opposed to spending their wrath over open ocean. One 2023 study in Nature Communications found that climate change and the rise in temperature in coastal waters has increased the number of rapidly intensifying hurricanes that strike just offshore by nearly four per decade from 1980 to 2020—a period in which global mean temperatures rose by nearly 1.5°C. “This suggests that global warming is a key driver of [rapid intensification] events,” the researchers wrote.

Climate change affects wind shear too—also making the planet more hospitable to hurricanes. The poles are heating faster than the equator and it’s the differential between those two regions that helps drive shear; the smaller that difference becomes, the calmer the upper atmosphere winds grow, allowing storms to build up force unimpeded. NOAA models predict that by the end of the century, the eastern part of the U.S. will be struck especially hard by this change—meaning more hurricane hits in unlikely places like western North Carolina, which was just devastated by Hurricane Helene.

But Helene has since moved on—leaving death and wreckage in its wake but at least passing into history. Milton is still barreling toward us—and no one is taking its approach lightly. “Helene was a wake-up call,” said Castor, the Tampa mayor. “This is literally catastrophic.”