An erratic North Atlantic hurricane season comes to an end this week, with an average number of storms, a rare quiet spell in August and destructive late-season activity, including the deadliest hurricane to hit the United States in nearly two decades.
The six-month season, which officially began on June 1 and ends on Wednesday, had 14 named storms, eight of which strengthened to become hurricanes. Two of these, Fiona and Ian, were major hurricanes, with maximum sustained winds of at least 130 miles an hour.
The totals are about average for a hurricane season. Some forecasters had expected an above-average season, although most predicted that the numbers for 2022 would remain below those for 2021, which had 21 named storms, and well below 2020, which set a record with 31.
The total of 14 storms was at the low end of predictions by forecasters with the National Oceanic and Atmospheric Administration, who said as late as August that there could be 14 to 20 named storms, including six to 10 hurricanes and three to five major ones.
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“We were one major hurricane short,” said the administration’s lead hurricane outlook forecaster, Matthew Rosencrans. They were also off in forecasting that the combined intensity of the entire season’s storms, a measure called accumulated cyclone energy, would be higher than it actually was.
Mr. Rosencrans said in August that the presence of the climate pattern called La Niña, which is characterized by unusually cool water temperatures in the equatorial Pacific Ocean, could lead to greater hurricane activity. In the Atlantic during a La Niña there is often less wind shear, and that allows tropical storms and hurricanes to grow stronger.
But Mr. Rosencrans said Tuesday that it appeared that there was significant wind shear during the season and especially in August, when no storms fully formed. Normally mid-August is the beginning of peak hurricane season, which lasts until mid-October.
The quiet August “was the real unforecast surprise of the season,” he said. A lack of moisture at high altitudes in the tropical Atlantic where storms begin their development may have played a role as well, he said.
Recent hurricane seasons have been marked by the development of one or more storms before the official start of the season. But this year, for the first time since 2014, there were no storms before June 1.
For two months, the season progressed slowly, with only three named storms by the end of July. This is not unusual; ocean waters are cooler and provide less of the energy that fuels storms. Hurricane activity picks up after the summer sun has warmed the ocean.
After the August lull, activity accelerated in September, with four hurricanes, including the two major ones.
In mid-September, Fiona slammed into Puerto Rico as a Category 4 storm. It dumped more than 30 inches of rain on parts of the island, leading to at least 25 deaths and further damaging infrastructure that had yet to be fully repaired after being damaged in Hurricane Maria five years before.
Two weeks later, Ian, another Category 4 hurricane, struck Florida with winds as high as 150 m.p.h. Together with rain and wind-driven tidal surges, that led to at least 114 deaths, most of them in the southwestern part of the state. It was Florida’s deadliest storm in nearly a century, and the deadliest in the United States since Katrina killed more than 1,800 people in southern Louisiana in 2005.
The season was notable in several other ways. Two storms crossed from the Atlantic basin to the Pacific, traversing Central America. The last time any storm did this was in 2016. “That is quite a rare phenomenon,” Mr. Rosencrans said.
And earlier this month, the season’s last storm, Hurricane Nicole, became the first to strike Florida in November in nearly four decades. While at Category 1 it was not as strong Fiona or Ian, it hit in some of the areas severely damaged by Ian just six weeks before.