Tropical Storm Michelle gaining strength.(Knight Ridder Newspapers)

MIAMI _ Michelle, a late-season tropical storm, crawled through the southwestern Caribbean Thursday night as forecasters watched for signs of an eastward hook that would take the strengthening system over Cuba this weekend _ and possibly on toward South Florida.

The National Hurricane Center said the most likely scenario puts Michelle at hurricane strength over western Cuba around noon Sunday, followed by a turn to the east or northeast. After that the path remains uncertain, mainly because of weak steering currents.

Most of the computer models that forecasters rely on indicate that Michelle _ a fairly compact storm at 115 miles across _ could cut through the Florida Straits, brushing the Keys, or veer slightly more north into the mainland.

Other models, considered less likely, show Michelle could continue on its current northward track toward the Panhandle or even turn west and strike Mexico.

"We want people to monitor this closely, especially if you're in the Florida Keys," said Max Mayfield, director of the hurricane center in west Miami-Dade. "We don't want to overdo it, but at some point, this storm is going to pick up speed. We don't want people to ignore the potential."

Mayfield said forecasters are also monitoring a trough of low pressure now over the Northeast. It is expected to dip down and help steer the storm in a more easterly direction.

The storm was located about 345 miles south-southeast of the western tip of Cuba on Thursday night, with winds of 65 mph. It was moving to the north-northwest about 5 mph.