Hurricane Milton, poised to make landfall on the Florida coast, arrived with a dramatic escalation. What was a mere tropical storm on Sunday, roared into Category 5 status on Monday with sustained winds of 180 mph, before slightly weakening on Tuesday. This rapid intensification begs the question: just how close are we to the theoretical maximum wind speed a hurricane can achieve? And is there a hard limit?
There is indeed a ‘speed limit’ on sustained wind speeds known as maximum potential intensity. However, it’s not a fixed number. It’s dictated by various factors, with the heat present in the ocean being a key driver. Current calculations place the maximum potential intensity for storms around 200 mph. But this is a dynamic figure that could change in the coming decades as oceans warm due to climate change.
Kerry Emanuel, an emeritus professor of atmospheric science at MIT, notes that the potential for strong storms has already been on the rise over the last 30 years. In fact, five recorded storms have exhibited winds exceeding 192 mph, all occurring since 2013. He predicts that by the end of the century, if we don’t take significant steps to curb climate change, these wind speeds could push towards 220 mph.
So, what fuels these powerful storms? James Kossin, a retired NOAA climate scientist, explains that the ocean is the source of their energy. The warmer the ocean water, the more fuel available for the hurricane. Other factors influencing maximum potential intensity include the heat in the atmosphere, the temperature of cloud tops (which affects heat transfer), and wind shear (the difference in wind speed and direction at different heights).
While a storm’s maximum potential can be calculated, it’s not always reached. Studies show that only 20% of Atlantic cyclones reach 80% or more of their potential. However, there is growing evidence that more storms are getting closer to their theoretical limits.
This trend is concerning, as the warming oceans and atmosphere are already driving stronger storms. Kossin and his colleagues reported that the proportion of major hurricanes increased by 8% per decade between 1979 and 2017. This means that powerful and rapidly intensifying storms like Milton could become far more common in the future.
The current hurricane classification system, the Saffir-Simpson Scale, only goes up to Category 5. This scale, however, doesn’t fully capture the damage potential of storm surge and flooding, which are often deadlier than wind. To address the increasing intensity of storms, Kossin and Michael Wehner from Lawrence Berkeley National Laboratory proposed a ‘Category 6’ in February, encompassing storms with winds over 192 mph. Five storms have already met this criteria, with Hurricane Patricia in 2015 being the most intense, reaching winds exceeding 200 mph.
While a ‘Category 7’ was considered, calculations showed it to be currently unlikely, but the possibility remains as the climate continues to warm.
The exact dynamics of the eyewall, the central region of a hurricane with the strongest winds, are still not fully understood. This complexity makes it difficult to predict the exact maximum wind speed a hurricane could achieve.
Hurricane Milton’s weakening after an eyewall replacement demonstrates the dynamic nature of these storms. Eyewall replacement, where a new band of thunderstorms forms around the eye, can deconcentrate the storm’s energy, reducing peak winds. Whether similar phenomena will become inevitable at extreme wind speeds is still an area of research.
As the world warms, the potential for storms with unprecedented wind speeds becomes increasingly real. The question remains: will these theoretical limits be surpassed, and what will the consequences be for our planet?
