Hurricane Ike was upgraded to an 'extremely dangerous' Category 4 storm by the National Hurricane Center late Wednesday as the system roared west across the central Atlantic.

Ike went from a tropical storm to a Category 4 hurricane in a matter of hours, Reuters reported.

The latest advisory from the National Hurricane Center, issued Thursday, increased Ike's maximum sustained winds to 145 mph, with higher gusts. Hurricane-force winds extended 35 miles from the storm's center of circulation.

The storm is sweeping across the open waters of the west-central Atlantic 550 miles northeast of the Leeward Islands, and is moving west-northwest near 17 mph, Reuters reported.

The hurricane center's official forecast puts Ike on a path toward the south Florida coast sometime early next week, though the storm's path and strength can change without warning.

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It is too soon to say whether Ike will threaten U.S. oil and natural gas producers in the Gulf of Mexico, Reuters reported.

Other storms in the Atlantic have become less of a major threat. Hanna, once a hurricane, weakened to a tropical storm near the Bahamas, and is foercast to strike the southeastern U.S. as a Category 1 hurricane by the end of the week.

Beyond Ike in the Atlantic, Tropical Storm Josephine had winds of 50 mph, but appeared headed northwest into open seas, where it would weaken in the coming days.

Ike is the fifth hurricane in the Atlantic this season.

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Tropical Storm Hanna knocked out power to the southern Bahamas on Wednesday and officials from Nassau to South Carolina warned residents to prepare for possible evacuations as it moves north and grows back into a hurricane, possibly Thursday.

The storm, packing 70 mph winds, turned to the northwest after lingering for days near Haiti, where it caused flooding that killed 61 people.

The Civil Protection Department reported that flooding is responsible for most of the deaths.

Department spokesman Abel Nazaire says 21 of the deaths were in Gonaives. That northern city has been almost entirely cut off by floodwaters from the storm.

Only a few dozen of the Bahamas' roughly 700 islands are inhabited, but they are near sea level and have little natural protection. The storm was expected to pass near or over the central Bahamas on Thursday before reaching hurricane strength.

But the National Hurricane Center in Miami warned its reach was expanding, with tropical-storm force winds extending up to 290 miles from the center.

"Hanna has become a large tropical cyclone," the center said.

Forecasters said Hanna could bring moderate to heavy rains to the east coast of Florida by Friday morning. Long-range forecasts call for the storm to hit anywhere from Georgia to North Carolina on Saturday and curve along the U.S. Atlantic coast.

On Wednesday, South Carolina Gov. Mark Sanford said he was returning from the Republican convention in Minnesota to deal with the storm.

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The Associated Press contributed to this report.