At 11 a.m. this morning, the National Hurricane Center reported Danielle reached Category 4 status with maximum sustained winds at 135 mph.

Forecasters are saying that Danielle will weaken as it moves north and hits cooler water and wind shear, but the same may not be true for Earl. Since its predicted track is more to the south, Earl may not be affected by the cooler water temperatures, which are not conducive to storm strengthening.

The National Hurricane Center's five-day track calls for Earl to reach hurricane status sometime Sunday morning, and it could affect Puerto Rico by Tuesday.

At the same time, the National Hurricane Center is keeping an eye on what it calls "a vigorous tropical wave" off the coast of Africa, about 210 miles to the south of Cape Verde Islands. Because environmental conditions remain favorable, the National Hurricane Center said there is a 70 percent chance this system will develop into a tropical depression during the next two days.

If this system reaches tropical storm status, it would be the sixth named storm of the year. The next name on the list is Fiona.

The peak of the hurricane season is considered to be late August through October, according to the National Oceanic and Atmospheric Administration (NOAA). Each of the 15 costliest hurricanes in U.S. history has occurred during this time frame with the exception of Hurricane Charley, which struck Florida on Aug. 13-14, 2004. Hurricane Katrina, which caused more than $41 billion in insured losses when it occurred, affected the Gulf States from Aug. 25-29, 2005.

Early in August NOAA said conditions were ripe for an active season and predicted 14 to 20 named storms, eight to 12 hurricanes, and four to six major hurricanes with at least Category 3 status. A Category 3 storm has sustained winds of 111 mph.