Hurricane Danielle strengthens to Category Four

"Danielle is a Category Four hurricane on the Saffir-Simpson (five-step) scale," the NHC said in a bulletin shortly before 0900 GMT.

"Some additional strengthening is possible in the next 24 hours."

The hurricane -- the second and strongest of the 2010 Atlantic hurricane season -- is forecast to track well east of the islands of Bermuda and then curl to the northeast and out to sea, but the NHC said "interests in Bermuda should monitor the progress of Danielle."

The weather system is not expected to hit the United States, although the NHC warned that large surf and dangerous rip currents were likely to affect parts of the US East Coast by Saturday.

Danielle surged in strength in just a few hours from Category Two to Category Four, the second highest level on the NHC's scale.

Category Four storms cause "catastrophic damage" when they make landfall, with "a very high risk of injury or death to people, livestock, and pets due to flying and falling debris," according to the NHC.

Shortly before 0900 GMT the hurricane was 875 kilometers southeast of Bermuda and moving to the northwest at 19 kilometers per hour, but there were no coastal watches or warnings in effect, the center said.

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