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Forecasts Mounting For Another Busy Atlantic Hurricane Season

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NOAA
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On Sept. 14, 2020, NOAA satellites photographed five storms in the Atlantic and Gulf of Mexico. The season set a new record with 30 named storms and the most landfalls since 1916.

Colorado State University issued its forecast Thursday, calling for another above average season — the second this week to predict a bustling season.

Another gloomy forecast issued Thursday is calling for the Atlantic to once again stir up a busier than usual hurricane season.

Colorado State University, which has been issuing forecasts for nearly 40 years and typically marks the approach of the season, expects 2021 to be above average with at least 17 named storms. Of those, eight could become hurricanes and four could intensify to major hurricanes, churning out powerful winds topping 111 mph.

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Meteorologists based the forecast on the low odds of an El Niño weather pattern developing in time to slow the peak of the season, beginning in mid August.

“Unfortunately, we don't think those conditions are going to be present this summer,” said Phil Klotzbach, an atmospheric scientist who took over writing the forecast in 2006.

Warmer than normal ocean waters are also expected to fuel storms, he said.

Earlier this week, AccuWeather issued a similar prediction, calling for 16 to 20 named storms, with seven to 10 becoming hurricanes. They forecast three to five powering up to major Cat 3 storms. The National Oceanic and Atmospheric Administration Climate Prediction Center typically issues its preseason forecast in May.

If it pans out, the season will make the sixth above-average season in a row and follows a record-breaking year that produced 30 named storms and forced the National Hurricane Center to turn to the Greek alphabet for names. In March, the center announced it was creating an back-up list, with an additional 21 names. The first storm of 2021 will be named Ana.

The busy streak can largely be attributed to the tepid El Niños. El Niños warm Pacific waters, which can increase upper level winds that shred hurricanes in the Atlantic.

“We haven't had a significant El Niño event during the peaks of the hurricane season since 2015, which was a very strong El Niño,” Klotzbach said.

Those led to mild upper winds blowing over warmer than normal waters that provided plenty of fuel for storms and are usually associated with lower pressure. That unstable atmosphere, he said, “helps create conditions that are more conducive for an active season.”

This year, Klotzbach said waters in the tropical Atlantic, where stronger systems typically form, are near normal. But to the north, waters around Florida and to the north in the subtropical Atlantic are above normal.

That’s likely going to repeat the scenario where warm waters set up low pressure and weak winds.

Without winds, the ocean mixes less, he said, so deeper cooler water won’t be mixing as well with upper, hotter water, leading to warmer tropical waters as the season peaks.

Climate change is partly to blame for the warmer ocean waters, he said. Globally, temperatures are higher across the tropics, helping fuel more powerful storms.

“With regards to El Niño, there doesn't seem to be much of a relationship there. When you get a strong El Nino, often it takes a little while to get another strong El Niño,” he said.

Atlantic hurricane seasons on average produce a dozen named storms, with six hurricanes and three major storms. But with numbers mounting in recent years, that average is shifting. The hurricane center is expected to update that baseline in May.

Klotzbach said his April forecasts have been off the mark, on average, by three in the past. The number drops to two by June and August, but he expects better modeling to improve that.

This year, National Hurricane Center forecasters will also be using improved storm surge models that they expect to provide more accurate surge warnings between 36 and 60 hours before landfall.

While track forecasts have been improving, and shrinking the cone of concern that depicts where a system could land, the size of the 2021 cone is not expected to change, the center said.