A total of at least four tornadoes touched down in Florida during a spate of storms earlier this week, including the first one rated as an EF3 since 1988. That makes 17 tornadoes total for the Sunshine State so far this year, compared to the average of seven it would normally record by the end of February.

The reason for the amped-up tornado activity this winter? The same climate force that has been influencing weather patterns around the world: El Niño.
 


El Niño is defined by the shifting of warm waters from west to east in the tropical Pacific Ocean. That shift changes where heat from those waters is pumped into the atmosphere, altering circulation patterns in a way that can affect the weather thousands of miles away.

Over the U.S., it shifts the subtropical jet stream — a fast-moving current of air — southward, and puts Florida in a prime position for tornado activity.

Tornadoes are a fickle phenomena, requiring just the right combination of ingredients to come together. Because of its proximity to warm ocean waters, Florida always has two of these ingredients — moisture and unstable air masses — on hand.

By tweaking the position of the jet stream, El Niño tends to bolster that second ingredient while also adding a third: the winds that are needed to spur the rotation that can spin up into a tornado, said John Allen, an associate research scientist at the International Research Institute for Climate and Society at Columbia University.

All of these ingredients have been on display throughout the winter in Florida.

“Things definitely seem to be going the way we would expect during a strong El Niño,” Allen said in an email. He and his colleagues at Columbia last year began an experimental seasonal tornado forecast, based on the links they saw between El Niño and tornado activity in the U.S.

While it can give a boost to activity in Florida, El Niño actually tends to tamp down activity in the more traditional Tornado Alley region, because the altered location of the jet stream cuts off the moisture from the Gulf of Mexico that helps fuel storms.
 


This year’s strong El Niño led the team to forecast a below-normal number of tornadoes in the south central U.S.

The extra oomph provided by El Niño also seems to boost the odds of having stronger tornadoes in Florida, or those that rank a 2 or higher on the Enhanced Fujita scale, a relative rarity for the state. Already this winter the state has not only clocked that EF3, which struck in the Panhandle just across the Alabama border, but a couple EF2s as well.

Florida’s deadliest tornado outbreak on record actually occurred in February 1998, in the midst of the last strong El Niño, state climatologist David Zierden said. During the event, 12 tornadoes touched down in Central Florida, killing 42 people, injuring hundreds and causing $100 million in damage.

But El Niño doesn’t guarantee big tornado activity, as other climate factors can come into play. Zierden pointed to 2010, when there was a moderate El Niño, but another climate pattern centered on the North Atlantic “overwhelmed the usual El Niño impacts and brought record cold to Florida. For much of the winter, temperatures were too cold to provide the instability needed for severe weather.”

How climate change might influence tornado activity in Florida and the U.S. as a whole is an open question and an active area of research at the moment. Some work has suggested that tornado activity might be concentrated into fewer days and that the peak of the season could be shifting earlier.