A tenacious Hurricane Epsilon strengthened slightly Monday as it lingered in the open Atlantic, posing no threat to land.

The 26th named storm of a record-breaking hurricane season had top sustained winds near 80 mph, up from 75 mph earlier in the day, according to the National Hurricane Center in Miami.

Despite being in cooler waters, Epsilon "refuses to weaken," hurricane specialist Lixion Avila said. "It means we still have a lot to learn about hurricanes."

But it was expected to turn southwest to areas with higher disruptive wind shear over the next day or two, he said, and "once it starts moving to the southwest, it's going to die."

The storm had been downgraded early Sunday to a tropical storm with sustained winds of 70 mph but unexpectedly regained hurricane strength of 75 mph. Epsilon first reached hurricane strength Friday and is the 14th hurricane of the season.

At 10 a.m. EST, the center of Epsilon's large eye was about 545 miles west-southwest of the Azores and moving east-southeast near 8 mph.

The Atlantic hurricane season began June 1 and officially ended on Wednesday.

Epsilon was only the fifth hurricane to form in December in more than 150 years of records, the hurricane center said. The latest that a hurricane has formed in the Caribbean was Dec. 30, in 1954.