Why do hurricanes even exist? The science behind these monster storms

Hurricanes have pummeled sea and land on Earth for eons — but why do these meteorological monsters even exist?

Simply put, hurricanes are the atmosphere's attempt to move heat from the warm equatorial regions toward the cold polar regions, meteorologist Phil Klotzbach of Colorado State University said.

It's one of the ways the atmosphere keeps its heat budget balanced, he added. In the winter, that can be done by storms like nor'easters or blizzards, while in the summer it's through hurricanes.

Tropical cyclones — an umbrella term that includes tropical storms, hurricanes, typhoons and cyclones — are giant engines that convert the energy from warm air into powerful winds and waves, according to NASA. That's why they only form over warm ocean waters near the equator.

The tropics near the equator supply the key ingredients needed for tropical cyclones: wide expanses of warm ocean water, air that's both warm and humid, and normally weak upper-air winds blowing from the same direction as winds near the surface, noted Jack Williams in the USA TODAY Weather Book. 

Hurricanes also tend to be most intense and frequent in the late summer and early fall, when ocean water is at its hottest, Massachusetts Institute of Technology hurricane expert Kerry Emanuel said in an interview with the Annenberg Foundation.

From a physics standpoint, he said a hurricane is a "heat engine. It's a massive, natural machine for converting heat energy into mechanical energy — the mechanical energy being the energy of the wind."

In addition, hurricanes don't just transport heat to the poles: "They also help radiate that heat out of the tropics into space," meteorologist Ryan Maue said.

Klotzbach added the storms also provide a small percentage — around 2% — of global rainfall during the peak months of the hurricane season in late summer and early fall. While that number seems small, hurricanes can account for 20-25% of rainfall in specific parts of the world, such as areas near the northwestern Pacific, he said.

However, tropical cyclones only account for about 10% of global heat transfer toward the poles, according to Klotzbach. Other equatorial waves, such as the Madden-Julian Oscillation, also play an important role in shifting heat around, he said. That oscillation is a huge, slow-moving atmospheric wave that stretches at least halfway around the globe on both sides of the equator.