How did Hurricane Polo get so powerful?

A Pacific cyclone dubbed Polo exploded from a tropical storm into a powerful Category 5 hurricane in less than 24 hours on Tuesday (Sept. 22), with winds reaching speeds of 180 mph (290 km/h). Now drifting off the southwest coast of Mexico, Polo has been downgraded to a Category 4 storm but remains "a very powerful major hurricane," the National Hurricane Center (NHC) said in an update Wednesday (Sept. 23) .

As Polo moves northwest, it is expected to drive torrential rainfall on parts of Mexico's southwest coast. Although the storm is not predicted to make direct landfall, the NHC has warned that heavy rain may produce life-threatening flooding and mudslides , as well as extremely hazardous ocean conditions.

Polo is one of the most powerful storms of the Pacific hurricane season so far, which runs from May to November. But what causes a hurricane like Polo to intensify so rapidly? And what role has the "super" El Niño played in the storm's development?

"Rapid intensification of tropical cyclones is something we see several times per year across the globe," Julian Heming , an environmental scientist and researcher at the U.K.'s Met Office, told Live Science in an email. "The main requirements are high sea temperatures, low wind shear and upper air conditions which allow air to escape quickly from the top of the hurricane."

Hurricane Polo intensified rapidly as it moved over exceptionally warm Pacific waters associated with an extremely strong "super'" El Niño that has taken hold off the Pacific since June .

El Niño is a naturally occurring climate pattern that develops in the tropical Pacific Ocean, typically every two to seven years. It begins when waters in the eastern tropical Pacific become unusually warm. The National Oceanic and Atmospheric Administration identifies El Niño conditions when these waters are at least 0.9 degrees Fahrenheit (0.5 degrees Celsius) above average, alongside changes in winds, surface pressure and rainfall that are consistent with the phenomenon.

El Niño events are then classified by strength, ranging from weak to very strong. Although "super El Niño" is not a scientific term, it refers to a very strong El Niño, where the warming of sea surface temperatures is higher than 2C above normal.

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