When Tropical Storm Gabrielle formed on Wednesday, it ended a nearly monthlong period of quiet in the Atlantic hurricane season during what is usually its most active time.
It was the second year in a row that what is known as peak hurricane season — when most hurricanes and the most destructive hurricanes typically form — began quietly, and like last year, some forecasters who had predicted this year would have an above-average number of named storms have been on edge.
Were their predictions wrong? Or would the Atlantic suddenly spin into action as it did last year, when Hurricane Helene and then Hurricane Milton, two of the most devastating storms in recent memory, formed within weeks of each other?
Here’s a look at what’s been keeping this year’s season quiet, and why that may be about to change.
Forecasters expected more storms than usual.
The Atlantic hurricane season runs from June 1 to Nov. 30, and there have been seven named storms this year. Only one storm, Erin, reached the threshold to become a hurricane, but its center remained far offshore.
Meteorologists have a name for hurricanes that stay away from land: fish storms, because they do nothing except disrupt the fish. Still, as with Erin, a distant hurricane can bring damaging rip currents and surf to the East Coast, so forecasters, state officials and residents need to track them closely.
In late May, the National Oceanic and Atmospheric Administration said in its annual prediction that its experts expected an above-average hurricane season, with between 13 and 19 named storms. An average Atlantic hurricane season has 14 named storms, including seven hurricanes.
What followed instead was one of the slowest starts to hurricane season in 20 years, with the first named storm, Tropical Storm Andrea, not forming until June 23.
At the season’s midpoint in early August, NOAA issued an updated forecast that only slightly reduced the number of storms expected. The ingredients were there for an above-average season, the agency said, and it expected between five and nine hurricanes to be packed in before the season ends on Nov. 30.
On Tuesday, Phil Klotzbach, a hurricane researcher at Colorado State University, said that the year could still be above average, which would mean more than half a dozen named storms between now and the end of November.
“Of course, my forecast confidence isn’t high at the moment,” he said. “If you had sent me an email last year on this date and asked how busy we thought October would be, I would probably have been tentative there, too.”
What’s keeping the storms at bay?
Weather conditions in the Atlantic have thwarted the development of storms for much of the summer.
Last year, the temperature of the Atlantic Ocean was abnormally high, which helped fuel an unusually intense hurricane season. This year’s temperatures aren’t as high, but they are still above average, and the water is certainly hot enough for hurricane development.
In recent weeks, though, wind shear, or the changing of wind speed and direction with height, has kept storms from forming. Think of it like trying to build a tissue tower in the middle of a circle of 20 industrial fans at different speeds and heights.
That shear is forecast to weaken, Dr. Klotzbach said, adding that he expected activity in the Caribbean to be above normal late in the season.
“We would anticipate October being fairly busy,” he said.
La Niña could play a role here, too.
Matt Rosencrans, the lead hurricane season forecaster with NOAA, said this week that after Gabrielle there would most likely be another storm soon on the horizon, and at least one more after that. “To have three more hurricanes before the end of September is not out of the question,” he said.
“Sixty percent of the hurricane season happens after that Sept. 10 peak,” Mr. Rosencrans said, analyzing data dating back to the 1850s. “It’s backloaded.”
As in previous years, the autumn half of hurricane season could be much busier than the summer months. Climatologically, Mr. Rosencrans said, the Gulf of Mexico and the Caribbean tend to “heat up with activity” from October into early November, while activity in the rest of the Atlantic begins to decline.
Another concern is that the weather pattern known as El Niño Southern Oscillation — known in the weather world as ENSO — is favored to turn toward La Niña. If this were to occur in the next month, it would help to reduce the wind shear across parts of the Atlantic and allow for more storms to form.
Judson Jones is a meteorologist and reporter for The Times who forecasts and covers extreme weather.
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