Why Hurricanes Are Becoming More Intense
Idalia is expected to be the first hurricane to hit the U.S. this season
Hurricane Idalia made landfall in Keaton Beach, Fla., on Wednesday morning as a Category 3 storm, according to the National Hurricane Center. It was battering the state’s northern Gulf Coast with high winds and a powerful storm surge predicted to reach up to 16 feet in some areas. More than 30 Florida counties have issued evacuation orders.
It was the first Atlantic hurricane to hit the U.S. this season, a year when an above-average number of storms is expected because of extremely warm water in the North Atlantic. The National Oceanic and Atmospheric Administration has predicted 14 to 21 named storms with winds of 39 mph or greater, including six to 11 hurricanes with winds of 74 miles an hour or higher.
This year’s record-setting ocean temperatures are the result of decades of climate warming and an El Niño pattern that is releasing heat from the Pacific into the atmosphere and affecting ocean temperatures globally, according to Michael McPhaden, senior scientist at NOAA’s Pacific Marine Environmental Laboratory in Seattle.
Here’s a look at some of the physical forces that drive hurricanes, how they form and how both climate change and El Niño weather patterns affect their formation:
The water temperatures in the North Atlantic and Gulf of Mexico are acting as fuel for tropical storms, which begin their life as a region of low pressure. As the pressure system moves over warm surface waters, it sucks up heat energy from the ocean, creating moisture in the air.
If the conditions are right, a tropical storm forms with an eye of rotating winds and intense rainfall. Once wind speeds in the eye of the storm reach 74 miles an hour, forecasters call it a hurricane.
This year, an El Niño weather pattern has also formed in the Pacific Ocean, resulting in a slosh of warm water developing across the eastern Pacific against the South American coast. In most El Niño years, there are more hurricanes in the Pacific (where they are known as typhoons) because of the warmer surface water, and there are fewer hurricanes in the Atlantic.
El Niños also produce strong upper-level winds that blow east across the tropics into the Atlantic basin. These winds typically shear off the developing cloud layers of Atlantic hurricanes, preventing their formation. This year, however, the record-warm Atlantic surface temperatures are counteracting that weather pattern.
Hurricane intensity—a measure of wind speed—has risen over the past 20 years. Eight of the 10 most active years since 1950 have occurred since the mid-1990s. The number of major hurricanes—those rated Category 3 and higher—has also increased.