The official 2023 hurricane season forecasts were just released, and while the Atlantic may see an average storm season this year, a busier-than-normal season is forecast in the eastern Pacific, meaning heightened risks for Mexico and Hawaii.

A big reason is El Niño.

El Niño typically means trouble for the Pacific and a break for the Atlantic coast and Caribbean. But while this climate phenomenon is highly likely to form this year, it isn’t a certainty before hurricane season ramps up this summer, and that makes it harder to know what might happen.

It’s also important to remember that even in quiet years, a single storm can cause enormous destruction.

As climate scientists, we study how climate patterns related to the frequency and intensity of hurricanes – information that is used to develop seasonal forecasts. Here is a quick look at how El Niño affects storms and why it tends to cause opposite effects in two basins separated only by a narrow stretch of land.

It’s helpful to start by visualizing where tropical storms develop in each ocean.

In the North Atlantic, tropical storms typically form over the warm waters off eastern Africa. As they move westward, they often hit Caribbean islands before making landfall on the U.S. Gulf Coast and Eastern Seaboard, or they curve off into the Atlantic.

Those tropical storms and hurricanes have caused over a trillion dollars in damage in the U.S. since 1981. That damage is expected to continue to increase, both because warming global temperatures fuel stronger storms and because more people are building homes and businesses in harm’s way.

In the eastern North Pacific, tropical storms tend to form closer to land, between Mexico and Clipperton Island off Central America. They typically move to the northwest before turning westward out to sea, sometimes inundating the Mexican coast known as the Mexican Riviera. Longer-tracked Pacific storms that move into the central Pacific can affect shipping and hit Hawaii, as Hurricane Lane did in 2018.

While the Atlantic gets the most attention, largely because it gets more damage with more people and property in the way, the Pacific tends to get more storms, especially during El Niño years. It’s often a seesaw pattern, with a busy year in one basin and a quieter season in the other.

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