(Reuters) - Hurricane Maria has weakened to a Category 4 hurricane but remains  extremely dangerous  and is expected to retain this intensity until it makes landfall in Puerto Rico in a couple of hours, the U.S. National Hurricane Center said on Wednesday. Maria is about 50 miles (75 km) southeast of San Juan, Puerto Rico with maximum sustained winds of 155 mph (250 km/h), the Miami-based weather forecaster said. 