The National Oceanic and Atmospheric Administration (NOAA) is out with their official Atlantic hurricane season outlook, and it calls for above average storm activity, which would make this the sixth unusually active season in a row.
Why it matters: This hurricane season comes in the wake of the North Atlantic Basin’s most active season on record, with 30 named storms occurring in 2020, 12 of which struck the U.S., setting a benchmark.
- By the numbers: NOAA is forecasting a 60% chance of an above average season, with a 70% probability of between 13 and 20 named storms. Of these named storms, NOAA is predicting that between 6 to 10 will be hurricanes, and 3 to 5 major hurricanes of Category 3, 4, or 5.
Flashback: Of the 30 named storms last year, 13 were hurricanes, and seven were “major” hurricanes of at least Category 3 intensity. The U.S. saw about $44 billion in economic losses from tropical cyclones in 2020, less than in 2005 and 2017, according to Steve Bowen, the head of disaster insight at Aon.
- The hardest hit region last year was the Gulf Coast, particularly central and western Louisiana, where two hurricanes struck land within 25 miles of each other at different points in the season.
The big picture: A few main factors are behind the 2021 seasonal forecast, all of which point to an uptick in activity, though not as severe as last year. First, there had been, until recently, a La Niña event in the tropical Pacific Ocean, which tends to diminish the upper atmospheric winds over the tropical Atlantic.
- This climate phenomena can reduce wind shear over the tropical Atlantic, which is when winds blow with different speeds or direction with height. Shear can rip apart nascent tropical storms and hurricanes.
- The atmospheric effects of La Niña are likely to linger into much of the first half of the hurricane season, and if another such event redevelops by the fall, the season could be even more active than currently anticipated.
- In addition, ocean temperatures in key parts of the tropical Atlantic are running above average for this time of year, though not as mild as they were at this time last year.
Climate change’s influence on tropical cyclones, which is the general term for tropical storms, hurricanes, and typhoons, is increasingly detectable, according to scientific studies. Nearly a dozen of the storms in the Atlantic Ocean last year underwent a process known as rapid intensification, leaping across several intensity categories in a matter of hours.
- In a warming world, more frequent bouts of rapid intensification is expected.
- In addition, hurricanes are now moving more slowly, and may be weakening more slowly once they cross over land. They’re also dropping more rainfall than they used to, thanks to the added moisture from warmer ocean and air temperatures.
- Other forecasting groups that issue seasonal outlooks have unanimously called for an above average season, though not as busy as 2020 was. These include Colorado State University and AccuWeather.
Of note: A forecasting group at Penn State University, which came the closest to predicting the actual number of storms in 2020, is calling for a range between 9 and 15 named storms this season, with a best estimate of 12 named storms.
What’s next: Already, the season’s first named storm, which is likely to be a hybrid between a tropical and non-tropical cyclone, is expected to form east of Bermuda in the next few days, but won’t significantly affect any land areas.