Miami, Florida (CNN) -- Hurricane Igor, which quickly intensified over the weekend, was poised on Monday to become a Category 5 storm -- the most-powerful on the Saffir-Simpson scale that measures tropical weather.
The storm blossomed into a major Atlantic Ocean hurricane on Sunday with top winds of 150 mph (240 kph), but remained far from land, forecasters reported.
Igor, which started as a tropical storm on Saturday, rapidly intensified from a Category 2 to a Category 4 storm Sunday, according to the National Hurricane Center. Forecasters described it as "large and powerful."
As of 5 a.m. ET Monday, the storm was about 940 miles (1,515 kilometers) east of the northern Leeward Islands and was moving west at about 13 mph (20 kph), the Hurricane Center reported.
"Some fluctuation in intensity is likely during the next 48 hours, and Igor could become a Category 5 hurricane today," forecasters said.
Hurricane-force winds extended up to 40 miles (65 km) from Igor's center, and tropical storm-force winds can be felt up to 160 miles (260 km) outward, according to the hurricane center.
As of Sunday evening, no coastal watches or warnings were in effect, and the storm is expected to turn to the west-northwest by Tuesday.
While the storm is expected to stay north of the Caribbean islands, the islands could experience some wind and rain because of Igor's size, forecasters said.
Meanwhile, in the far eastern Atlantic, Tropical Storm Julia formed Sunday night. As of 5 a.m. ET, its center was about 60 miles (100 kilometers) south-southeast of the southernmost Cape Verde Islands
As a tropical depression, Julia was spreading rain over the Cape Verde Islands Sunday, forecasters said.
The storm's maximum sustained winds were at 40 mph (65 kph). It was moving west-northwest at 12 mph (19 kph).
"On the forecast track, the center of Julia will continue to move near the southernmost Cape Verde Islands this morning, and away from the Cape Verde Islands later today and tonight," forecasters said.
Some strengthening is expected, and the storm could become a hurricane on Tuesday.
Julia is expected to produce total rain accumulations of 2 to 4 inches over much of the Cape Verde Islands, with possible isolated maximum amounts of 8 inches, the hurricane center said. These rains could cause life-threatening flash floods and mudslides.