October is here. What does that mean for Atlantic hurricane season?

We’re still eight weeks out from the official end of the Atlantic hurricane season, but thus far, we’ve been lucky. Of the 18 named storms to spin up over the ocean, the fiercest — Lee and Franklin — remained mainly out at sea. Idalia, which struck the Lower 48 as a major hurricane, rapidly weakened upon landfall and mostly avoided populated areas. And has been the only hurricane to hit the United States this year.

Hurricane season historically peaks in mid-September, and activity statistically begins to simmer into November. But serious storms — often originating from the Caribbean or Gulf of Mexico — can form in October.

Florida and Louisiana are the two states that encounter October hurricanes the most. Southeastern Florida is particularly vulnerable. “It’s historically the month where we are mostly likely to have a hurricane encounter,” tweeted Brian McNoldy, a hurricane expert at the University of Miami.

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At present, Tropical Storm Philippe continues to drench the northern Leeward Islands, but otherwise the Atlantic is quiet.

To this point, the hurricane season has already produced about a full season’s worth of activity, but experts predict more storminess going forward. It’s possible the Gulf of Mexico or Caribbean could wake up in the weeks ahead.

Tracking Philippe

Tropical Storm Philippe has been wandering through the western tropical Atlantic for 10 days now and is about 80 miles east-northeast of St. Thomas in the U.S. Virgin Islands. It has winds of 45 mph and is heading northwest at 10 mph.

On Monday night, Philippe lashed portions of Antigua and Barbuda, Guadeloupe and Dominica with strong winds and heavy rain, triggering flash flooding.

Anguilla is under a tropical storm warning, while the British Virgin Islands are under a tropical storm watch.

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“Heavy rainfall from Philippe is expected to produce scattered flash flooding across portions of the northern Leeward Islands and the British Virgin Islands into early Wednesday,” the National Hurricane Center wrote Tuesday.

The storm has defied expectations crossing the Atlantic — traveling farther west than forecast. So while forecasters predict it will begin turning north and approaching Bermuda, it has a lengthy history of making up its own mind.

It’s probable that Philippe will pivot northwestward in the next seven to 10 days, perhaps affecting the Northeast or Canadian Maritimes as a nontropical low pressure system. It will be steered around a high-altitude pocket of low pressure over the northeastern Caribbean.

As I highlighted yesterday, it is quite likely that Tropical Storm Philippe will pivot counterclockwise (NE->N->NW) around a mid-level trough over the Bahamas and into Nova Scotia or possibly the NE US as an extratropical low pic.twitter.com/Upm9ytXSl7

What October could hold

Once Philippe transitions into a nontropical storm, what’s next for hurricane season?

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Philip Klotzbach, a hurricane researcher at Colorado State University, leads a team that publishes biweekly to seasonal forecasts.

His group is calling for “near-average October-November Caribbean Accumulated Cyclone Energy.” ACE, or Accumulated Cyclone Energy, is a measure of how much energy tropical storms and hurricanes extract from warm ocean waters and expend on winds. Predicting typical ACE essentially says that October and November should churn out close to the average number of storms.

October averages 2.75 named storms, and it’s not uncommon for hurricanes, and even major hurricanes, to form. This year, a nascent El Niño pattern could make high-altitude winds less favorable for development, but that should be offset by near-record warm sea surface temperatures.

Caribbean and Gulf of Mexico are areas to watch

In August and September, high-end and long-lived tropical cyclones more traditionally form over the Atlantic’s MDR, or Main Development Region. That’s the imaginary rectangle in the tropical Atlantic between Africa and the Caribbean Sea. The oceans are robustly warm.

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But in October, the jet stream, or a river of winds in the upper atmosphere, begins to swing farther south across the Atlantic. That spills strong high-altitude winds over the MDR, which disrupts storms that try to form. That’s why the MDR usually shuts off this time of year.

The Caribbean and Gulf of Mexico, meanwhile, are at their hottest, and shear isn’t yet too much of an obstacle. Sometimes, cold fronts that sink into the Gulf of Mexico shed disturbances that can act as seeds for tropical development.

“Storms that form down here often find an open channel northward courtesy of jet stream dips that accompany fall fronts down into the southern U.S.,” wrote Michael Lowry, hurricane expert for Miami television affiliate in WPLG in his Substack newsletter. “These 'weaknesses’ in the atmosphere tend to draw storms out of still-warm waters, giving them ample opportunity to strengthen on approach to land. Those hurricanes sneaking into the Gulf often get whisked northeastward by jet stream winds which make the protruding boot of south Louisiana and the Florida peninsula more susceptible to strikes.”

In recent years, rapidly intensifying October storms like Hurricane Michael, which made landfall as a Category 5 along the Florida Panhandle in 2018, have underscored the importance of remaining vigilant during the month. Other notable October hurricanes include Opal, which hit Panama City Beach at Category 3 strength in 1995; Category 4 King, which ravaged Miami in 1950; and Category 4 Hazel, which slammed the Carolinas in 1954. Notably, Wilma became the Atlantic’s strongest hurricane on record in the western Caribbean on Oct. 15, 2005.

Although Florida and Louisiana remain the most hurricane-prone states in October, everyone from Texas to the Mid-Atlantic should keep tabs on forecasts. While there’s nothing of immediate concern, it doesn’t take long for that to change.

Jason Samenow contributed to this report.

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