Category 4 is the second most powerful rating on the Saffir-Simpson Hurricane scale, which is a classification used for some Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms.
A storm this strong leaves a trail of destruction on its path as it is capable of causing heavy damage to buildings, trees and power lines.
With sustained winds of 135 mph, Hurricane Earl was about 110 miles northeast of San Juan, Puerto Rico, on Monday, Aug 30 evening.
US National Hurricane Center here has said that the hurricane moving at about 15 mph and is expected to turn northwest Tuesday, Aug 31.
Hurricane warnings are in place in the tourist popular-Caribbean Islands. Advisories warn of Earl intensifying over Tuesday, Aug 31 and posing as a threat.
People and businesses on the US mainland may also be hit as Earl is set to carve off the East Coast later in the week.