MIAMI -- Epsilon rapidly gained major hurricane strength on Wednesday afternoon and is expected to skirt east of Bermuda in the coming day, the U.S. National Hurricane Center says.

The Category 3 storm is packing top sustained winds of 115 mph (185 kph) and Bermuda remains under a tropical storm warning. Epsilon gained 50 mph (80 kph) in wind speed in just 24 hours, officially qualifying as a rapidly intensifying storm. It is the seventh storm this season to power up this quickly.

The Miami-based hurricane centre said Epsilon was located at 8 p.m. EDT about 315 miles (510 kilometres) southeast of Bermuda, and was moving to the west-northwest at 10 mph (17 kph).

Forecasters said Epsilon should make its closest approach to Bermuda by Thursday afternoon or evening. Gradual weakening of the storm is expected to begin on Thursday and continue into the weekend.

Over the past couple decades, meteorologists have been increasingly worried about storms that blow up from nothing to a whopper, just like Epsilon. Forecasters created an official threshold for this dangerous rapid intensification -- a storm gaining 35 mph (56 kph) in wind speed in just 24 hours.

Forecasters said tropical storm conditions would soon begin on Bermuda and continue intermittently through late Thursday. Epsilon is expected to make its closest approach to the island on Thursday afternoon or evening, according to the U.S. National Hurricane Center.

Large swells generated by Epsilon are already affecting Bermuda, the Bahamas, the Greater Antilles, and the Leeward Islands, and are expected to cause life-threatening surf and rip current conditions along the coast of New England and Atlantic Canada during the next couple of days.

This year's hurricane season has had so many storms that the Hurricane Center has turned to the Greek alphabet for storm names after running out of official names.

Epsilon also represents a record for the earliest 26th named storm, arriving more than a month before a storm on Nov. 22 in 2005, according to Colorado State University hurricane researcher Phil Klotzbach.