El Niño Boosting South Florida’s Wild Winter Rains

Winter is supposed to be the dry season in South Florida, but that certainly hasn’t been the case for the past few days, as social media pictures of canoes on flooded roads can attest.

With more than 8.5 inches of rain since the beginning of the month, the Miami area has already experienced one of its wettest Decembers. Several locations have set rainfall records, and flash flooding has been a major concern.

“It’s been a lot of rain,” Chuck Caracozza, a meteorologist with the National Weather Service office in Miami, said.

The repeated bouts of rain have come as disturbances have moved up along a stalled frontal boundary off the coast, but a strong El Niño is playing a role as well.

During the cold season, El Niño boosts the subtropical jet stream that flows over the southern tier of the U.S., leading to wetter-than-normal winters there.

In the case of the recent rains in South Florida, “the subtropical jet helped stream in moisture from the tropical Pacific,” Florida state climatologist David Zierden said in an email. Lots of moisture means lots of rain.

El Niño tends to bring about 40 to 50 percent more rain than normal to South Florida during the winter months, Zierden said. During the similarly strong El Niño of 1998, the region “crushed the record for November-March rainfall at over 33 inches, nearly three times normal,” he said.

The potential role of climate change in boosting the chances of such a considerable rainfall event in this area hasn’t been evaluated, but warming is expected to make heavy rain events more likely, as a warmer atmosphere holds more moisture. Florida, like the U.S. as a whole, has seen an increase in heavy downpours in recent decades.

The National Oceanic and Atmospheric Administration seasonal forecast for Florida for December through February has a 74 percent chance of above-normal rains this winter, “one of the strongest seasonal forecasts they have ever issued,” Zierden said.

Though El Niño’s strongest effects on the U.S. are mostly confined to the winter months, this event may have also played a role in the drought in South Florida during the summer. El Niño tends to bring drier conditions to the Caribbean during the summer, and “it seems as if the Caribbean dryness may have extended up into south Florida this year,” Zierden said.

That drought is long gone now.

As of Monday morning, Miami International Airport had already hit its second wettest December on record, with 8.48 inches of rain. The record for the whole month, set in 1929, is 9.03 inches.

Considering how much of the month is left to go and the increased odds of more wet weather, “there is a good chance” that record could be broken, Zierden said.