The science of how Hurricane Milton became such a monster

Hurricane Milton caused surprises at almost every turn.

What began as a small, tightly coiled hurricane has become a sprawling monster, strengthening at one of the fastest rates in history. The storm threatens to unleash a dangerous wave of water on parts of Florida's west and east coasts, with the flood-prone Tampa Bay metropolitan area, home to more than three million people, particularly at risk.

As the storm developed, record warm seas in the Gulf of Mexico contributed to its intensification. It later grew in size as the eye walls were replaced.

Here's how Milton became such a significant threat.

A Pacific influence

Hurricanes that approach the United States typically follow a similar path: Tropical storms begin on the west coast of Africa, cross the Atlantic, and grow stronger as they enter the warm waters of the Caribbean.

But part of Milton's origin story lies in the Eastern Pacific. The hurricane formed when the remnants of a tropical depression in the Pacific swept east across the Yucatan Peninsula and encountered a stalled front in the Gulf of Mexico. The most recent storm to hit Florida after forming in the same area – the Bay of Campeche in Mexico – occurred in 1867.

As the tropical depression moved into the Gulf, it offered a thunderstorm system there “a little bit of vorticity, that level of spin,” said Chris Slocum, a physicist at the National Oceanic and Atmospheric Administration's Center for Satellite Applications.

Then Milton organized himself and displaced other systems.

“It is this isolation from other thunderstorms that allows pressure to intensify and winds to develop,” Slocum said. Milton began drawing air into his center, drawing energy from the warm ocean.

Small but strong

Milton began as an extremely small storm, allowing it to maintain its angular momentum and rotate tightly and quickly around a narrow eye.

The Gulf encountered record-breaking sea temperatures and moist, warm air – the conditions for intensification. On Monday, the central pressure in Milton's core fell at a rate one scientist described as “crazy” while Milton grew stronger. Central pressure values ​​are closely related to the strength of a storm and its wind speeds.

“This is just terrible,” said John Morales, an NBC South Florida hurricane specialist, who choked up as he spoke about the significance of the pressure drop.

Wind speeds in Milton increased by 92 miles per hour in about 24 hours, according to Climate Central, a nonprofit research group. That far exceeded the milestone for what scientists call rapid intensification: a rise of 35 miles per hour in 24 hours.

“It went from a tropical storm to a Category 5 hurricane in less than two days, which is unimaginable,” said Karthik Balaguru, a climate scientist at the Pacific Northwest National Laboratory.

Jonathan Lin, an atmospheric scientist at Cornell University who predicts and models hurricanes, called Milton “one of the fastest-strengthening hurricanes we've ever seen in the Atlantic.”

The hurricane's wind speeds – which exceeded 175 miles per hour – were unprecedented for an October storm. Milton is the strongest hurricane in the Gulf of Mexico since Hurricane Rita in 2005.

A new eye wall

In the Northern Hemisphere, hurricanes rotate counterclockwise around mostly cloud-free eyes at their centers.

Bands of rain formed on the outer edge of Milton overnight Monday into Tuesday. These storms merged and formed a second ring, forming a replacement eyewall and tripling the radius over which maximum wind speeds were recorded, Slocum said.

This phenomenon, known as eyewall replacement, typically causes storms to gain width but lose some wind speed, which was the case with Milton. This can happen multiple times as a storm develops. Once the process is complete, the hurricane may regain intensity if conditions permit.

“You can think of it like shedding your skin. Once it sheds its skin, it can strengthen again. That’s exactly what we saw at Milton,” Lin said.

A wobble

According to the National Hurricane Center, Milton “wobbled” Tuesday afternoon, changing its planned trajectory and shifting its estimated landfall to the south.

Wobbling movements arise from instabilities due to complicated dynamics within the eye wall.

Lin explained the dynamics by comparing a hurricane to a spinning top or dreidel.

“Sometimes you see a top – you push it a little, nudge it, and it wobbles a little and then starts spinning again,” Lin said. “It’s reorienting itself.”

Significant fluctuation can change the track of a storm and determine which locations bear the brunt of the hurricane.

Meteorologists expect a storm surge of up to 13 feet. If the storm veers slightly south, it could keep the worst of the flooding away from particularly vulnerable Tampa Bay. Hurricane Irma moved eastward in 2017, which helped keep Tampa Bay from facing a forecast storm surge of 12 feet or more.

As the storm reaches the coast, areas south of Milton's Eyes should be affected by strong gusts that will push water onto the coast – and the resulting storm surge.