A Category Three storm has winds of 111 miles (179 kilometers) an hour to 130 miles (193 kilometers) an hour and is considered a major hurricane.
The storm had reached Category Four status yesterday, meaning that its strongest winds exceeded 130 miles (209 kilometers) an hour.
John is still moving over warm water and probably will regain Category Four status, Kimberlain says.
The storm's track will be determined by a high-pressure system to the north, he says.
According to predictions, John's centerand its strongest windswill most likely stay offshore until the hurricane turns away from land.
The hurricane is expected to make a sharp turn west late Saturday or early Sunday and rapidly lose strength.
"In about 36 hours, as the center slips past the southern tip of the Baja Peninsula, it gets into really cold water," Kimberlain said. "The water temperature goes from being at a level that can support a hurricane to very cold. It will begin a steady weakening."
After it makes its turn, John will head into the open waters of the Pacific Ocean and "meet its demise," Kimberlain said.
But a small eastward shift in the hurricane's course could send the storm slamming into Mexico and cause severe damage, officials warn.
John began last week as a tropical depression in the southwestern Caribbean Sea. The system crossed Central America into the Pacific and quickly developed into a powerful hurricane.
Meanwhile, another hurricaneKristyhas formed in the Pacific. The storm, currently packing winds of 75 miles (120 kilometers) an hour, is expected to remain at sea.
Willie Drye is author of Storm of the Century: the Labor Day Hurricane of 1935, published by National Geographic.
Free Email News Updates
Best Online Newsletter, 2006 Codie Awards
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES