Tropical storm Igor grew into a low-level hurricane overnight, becoming the fourth hurricane to form during the 2010 Atlantic season.

The storm is strengthening quickly. In an early morning advisory, the National Hurricane Center in Miami pegged the storm's maximum sustained winds at about 80 miles an hour. As of the 10 a.m. Eastern Daylight Time outlook, Igor was packing maximum sustained winds of 105 miles an hour, spinning some 1,145 miles east of the northern Leeward Islands, according to the hurricane center's forecasters.

Hurricane-force winds extend some 35 miles from the center, while tropical-storm-force winds extend as far as 140 miles

Forecasters say they expect the storm to strengthen significantly within the next 12 hours, achieving maximum sustained winds of 110 miles an hour or more.

If that occurs, Igor would become the third major hurricane to form this season. By Monday, the storm could strengthen to category four storm, with maximum sustained winds of between 131 and 155 miles an hour.

Igor first appeared as a broad patch of thunderstorms off the western Africa coast. On Sept. 8, the storm system quickly became more organized and more powerful, leapfrogging tropical-depression designation to become a tropical storm and the ninth named storm of the season.

Yet as if to suggest Igor still had to pay its dues, conditions weakened the storm for about a day and a half, dropping it back to tropical depression status.

Now, Igor's back and growing. The current forecast track puts the center of Igor some 600 to 700 miles east of the Bahamas by Friday morning, although there is significant uncertainty in the storm's predicted position that far in advance.

Meanwhile, Igor has company. Forecasters also are tracking tropical depression 12, which formed Sunday morning from another angry cluster of thunderstorms off Africa. It could well reach tropical storm status and become a hurricane by Tuesday morning. Tropical storm warnings have been issued for the southern Cape Verde Island.