Otto gained strength in the Caribbean on Tuesday to become the seventh hurricane of the season so far and the latest hurricane on record in the Caribbean Sea. An “average” Atlantic hurricane season ends Nov. 30.

A hurricane watch is up for Costa Rica and southern Nicaragua, and a tropical storm watch has been posted for Panama.

“These are startling locations for tropical cyclone advisories–understandably so,” Bob Henson wrote on Tuesday. “A storm of Otto’s expected strength has never made landfall so far south in the Caribbean, and there is no record of any hurricane striking Costa Rica.”

Otto formed on Monday as a tropical depression but has strengthened into a formidable storm since then. Sustained winds could be around 90 mph when it makes landfall early Thursday.

We wrote yesterday that when a hurricane forms this late in the season, it’s probably going to be in the western Caribbean. But Otto is late even for this region.

Looking back at the historical record, very few storms have formed so late. Otto is the latest hurricane on record in the Caribbean. And across the Atlantic, since 1851, just 35 storms that reached tropical storm intensity on or after Nov. 15. That’s an average of about once every five years. The most recent was Melissa in 2013, and the strongest was Kate in 1985. Just half of those went on to reach hurricane intensity.

When Otto makes landfall Thursday, its biggest threat will be heavy rain and the resulting mudslides. Up to 18 inches of rain could fall in northern Costa Rica and southern Nicaragua. Luckily, this area of the coast is not packed with people.

After that, the storm looks like it will cross over into the Pacific, which doesn’t happen every day but is far from rare. It would be more interesting if a storm was crossing from the Pacific into the Atlantic.

“More than a dozen ‘crossover’ tropical cyclones have been recorded, most of them moving from Atlantic to Pacific rather than vice versa,” Henson wrote. “The most recent was Hermine (2010), which formed as an East Pacific tropical depression before entering the western Gulf and striking the northeast coast of Mexico as a tropical storm.”