How Rare Are November Hurricanes?

How Rare Are November Hurricanes?

November hurricanes and tropical storms such as Nicole are relatively rare, but they can–and do–form

Tropical Storm Nicole, a rare November storm, churns toward Florida on Nov. 9, 2022. Credit: CIRA/NOAA

November weather is a common occurrence in North America. It’s the time when autumn edges closer to winter, with cool breezes blowing through red, yellow and green leaves. This is not usually a time when people associate destructive tropical cyclones with the U.S., but that is exactly what is happening as Tropical storm Nicole bears down upon Florida, where it is expected make landfall as hurricane.

Though such tropical systems are less common at this time of year, the official Atlantic hurricane season actually lasts through November 30. And storms can form even after that point, as notably happened during the blockbuster 2005 season when Tropical Storm Zeta shockingly formed on December 20 and lasted until January 6.

Hurricane season begins June 1. It marks the time of year when ocean and atmospheric conditions are most favorable for storm formation. The season’s peak is at the end of August and early October. This is because ocean heat at the end of summer coincides well with wind conditions that are more favorable for storm formation. Jill Trepanier, a hurricane researcher from Louisiana State University, says that storm activity “starts declining pretty quickly once November 1st hits.” This means that November is the quietest month in terms of U.S. landfall activity, according to Ryan Truchelut (a meteorologist and cofounder of WeatherTiger), a private weather-forecasting company. Only 10 tropical storms and three hurricanes have struck the U.S. during November going back to 1851, he says, so on average such a landfall would happen about every 10 to 15 years.

There are years that are true outliers. Three November storms, one of them a hurricane, formed in 2005. More recently, “November was crazy in 2020,” Truchelut says, thanks to exceptionally warm waters in the Caribbean. Hurricane Eta hit Nicaragua as a category 4 storm, followed two weeks later by another category 4 hurricane, Iota.

Storms that form in November tend not to be as strong because they are rarer. Trepanier explains that as fall progresses, solar power shifts from the Northern Hemisphere into the Southern Hemisphere, and northern latitudes quickly cool down. This creates a big contrast with the lingering warmth farther south, strengthening the polar jet stream–which then sends incursions of cold air southward. These incursions increase wind shear, which is when winds change in speed and direction at different levels in the atmosphere. This disrupts the convection at their core.

Though Nicole will probably be relatively weak in terms of wind speed, its winds cover a large area and are thus expected to bring storm surge to the entire east coast of Florida. This coincides with a period when there are higher-than-normal high seas which will increase surge amounts.

Historically, November storms that hit the U.S. tend to strike Florida, Truchelut states, because they most often form in the western Caribbean. The most recent November hurricane to hit the state was Kate, which struck the Florida panhandle on November 22, 1985, as a category 2 storm. Nicole will be the first to set the record for the most recent storm to hit the state’s east coast. The previous record holder was the Yankee Hurricane, which made landfall near Miami Beach on November 4, 1935 (this was before meteorologists began giving official names to hurricanes and tropical storms).

Having a late-season threat from Nicole so relatively soon after Eta hit the state as a tropical storm in 2020–twice–raises the question of whether late-season storms will become more frequent as climate change brings warmer ocean waters, Truchelut says. A study he co-authored, published earlier this year in Nature Communications, looked for statistical evidence that the hurricane season might be growing longer at both ends. Though this research found strong evidence that the season is starting earlier, that evidence was weak for the end of the season. He notes that it is possible that there is a trend that cannot be detected yet because it is difficult to detect rare events

Nicole demonstrates that people in hurricane-prone areas must pay attention to forecasts and be ready to act on them, Trepanier states. “Driving home that point is important.”

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    Andrea Thompson, an ass

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