How strong can hurricanes get?

Hurricane Milton, expected to hit the Florida coast on Wednesday or early Thursday (October 9 or 10), seemed to come out of nowhere: On Sunday the hurricane was just a tropical storm, on Monday (October 9 or 10 ) he raged into category 5. 7), with sustained winds of 180 mph (298 km/h) before weakening slightly on Tuesday (October 8).

But how close is Milton’s sustained wind speed to the theoretical maximum? And is there a hard limit?

There is a “speed limit” to sustained wind speed, called the maximum potential intensity, but it is not absolute: it is determined by several factors, including the heat present in the ocean. Current calculations of maximum potential intensity for storms are typically around 200 mph (322 km/h).

But that could change in the coming decades as the oceans warm and the climate changes. The potential for strong storms has already increased over the past 30 years, he said Kerry Emanuela professor emeritus of atmospheric sciences at MIT who developed the model. This also applies to real monster storms: five recorded storms had wind speeds of more than 192 mph (309 km/h). All of this happened since 2013.

“I think by the end of the century the speed will be closer to 220 (mph) if we don’t slow down a lot,” Emanuel told Live Science.

Related: We may need a new Category 6 hurricane rating for wind speeds over 180 mph (300 km/h), according to a study

What drives a storm

The speed limit in hurricane winds is relative easy to calculatesaid James Kossina climate scientist who is retired from the National Oceanic and Atmospheric Administration (NOAA) and now works as a consultant for the climate risk modeling agency First Street.

“The fuel for hurricanes is the heat they take from the ocean,” Kossin said. “The warmer the water, the more fuel is available.”

An image of the equation used to calculate a hurricane's maximum wind speed.

A hurricane’s maximum wind speed is determined by the water temperature (Tocean), the temperature at the cloud cover (Taloft), and E, a factor that determines how quickly heat can be transferred from the ocean to the air. (Image credit: Created with CodeCogs Equation Editor)

Other factors help determine maximum potential intensity, such as the heat in the atmosphere and the temperature of cloud surfaces, which determine how quickly heat can move from the ocean surface to the top of a storm, and wind shear, the difference in the Wind speed and direction at different altitudes in the atmosphere. Too much wind shear can tear a storm apart, weakening it and preventing it from reaching its full potential. A Study of storms Surveys between 1962 and 1992 found that only 20% of Atlantic cyclones reached 80% or more of their maximum potential intensity, although there is evidence that a larger proportion of storms are beginning to approach their theoretical limit, Emanuel said.

As the oceans and atmosphere warm, the storms become stronger. This was reported by Kossin and his colleagues in 2020 the proportion of severe hurricanes increased by 8% per decade between 1979 and 2017. This means that as the climate warms, strong and rapidly intensifying storms like Milton could become frighteningly common.

New hurricane categories?

Hurricanes are classified on the Saffir-Simpson scale, which ranges from Category 1 (beginning with sustained wind speeds of 74 miles per hour or 119 km/hour) to Category 5 (beginning with sustained wind speeds of 157 miles per hour or 252 km/hour wind speed). ) suffices ). That scale is incomplete because it is based on wind speed and does not include damage from storm surges or flooding, which are deadlier than wind, Emanuel said.

The increasing likelihood of strong storms spurred Kossin and his colleagues Michael Wehner from the Lawrence Berkeley National Laboratory propose in February that the Saffir-Simpson scale may require a “Category 6,” which would include storms with winds exceeding 192 mph (308 km/h).

The researchers identified five storms that would already fall into this category: Typhoon Haiyan (2013), Hurricane Patricia (2015), Typhoon Meranti (2016), Typhoon Goni (2020) and Typhoon Surigae (2021). Patricia was the most intense on record and the only one with winds over 200 miles per hour. (The hurricane’s wind speeds reached 215 mph (345 km/h), but weakened to 150 mph (241 km/h) as the storm made landfall.)

Wehner and Kossin considered considering hurricanes in a theoretical “Category 7” with wind speeds above 229 mph (368 km/h). But their calculations showed there is currently a negligible risk of such a strong storm, Wehner told Live Science, so they left the possibility out of their paper.

No one really knows what maximum winds a hurricane could theoretically sustain if water temperatures continue to rise, Wehner said. “In these really strong, pronounced eyewalls where the winds are moving like crazy, these currents are very unstable,” he said.

The exact dynamics of the eyewall are not fully understood, Wehner said. Milton’s weakening occurred after an eyewall replacement. This occurs when a new band of thunderstorms forms around the eye of the storm and moisture drains away from the original eyewall. The shift deconcentrated Milton’s energy, increasing the storm’s overall size but also reducing its peak winds. It may be that these storm-weakening phenomena become unavoidable at extreme wind speeds, but that is not yet fully understood, Wehner said.

“Suppose we are in a world that is 4 degrees warmer, which is almost unthinkable, where the maximum possible intensity is well over 300 km/h,” he said. “Could these storms actually sustain themselves? I don’t think we know.”

Editor’s Note: This article was updated at 9:45 a.m. EDT on Wednesday, October 9, to correct the conversion from 200 miles per hour to km/hour.

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