Miami, Florida (CNN) -- Hurricane Igor maintained its Category 4 status Monday afternoon, still huffing and puffing top sustained winds of 150 mp (240 kph) although tracking maps show the storm remaining in the open Atlantic, far from land.

Behind it, Tropical Storm Julia strengthened and could become a hurricane with in the next day or so, the National Hurricane Center said. Julia, too, was moving away from land, although a tropical storm warning was in effect for the southern Cape Verde islands as the storm moved past.

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" but said it would likely drop to a Category 3 storm by the end of the week.

As of 5 p.m. ET Monday, Igor's center was about 830 miles (1,335 kilometers) east of the northern Leeward Islands. It was moving west at about 10 mph (17 kph).

Hurricane-force winds extended up to 50 miles (85 kilometers) from Igor's center, and tropical storm-force winds can be felt up to 195 miles (315 kilometers) 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 p.m. ET Monday, its center was about 210 miles (335 kilometers) west of the southernmost Cape Verde Islands, but the storm was pulling away from the islands.

The storm's maximum sustained winds were at 50 mph (85 kph). It was moving west-northwest at 14 mph (22 kph).

Additional rainfall of 1 to 2 inches are possible over the northwest portion of the Cape Verde Islands, with isolated maximum amounts of 4 inches possible in some locations, forecasters said. These rains could cause life-threatening flash floods and mudslides.

Tracking maps show Julia becoming a Category 1 hurricane over the open Atlantic later in the week before dropping back to tropical storm intensity without nearing land.