MIAMI (CNN) -- Tropical Storm Katia was strengthening in the Atlantic Ocean on Tuesday and could become a hurricane on Wednesday, the National Hurricane Center said.

In its 4:00 advisory this afternoon, the hurricane center said Katia has maximum sustained winds of 60 mph – up from 45 mph six hours earlier. The storm was in the open Atlantic about 750 miles west of the southernmost of the Cape Verde Islands, which are hundreds of miles off the west coast of Africa.

Katia was moving west-northwest near 20 mph. That general motion was expected to continue for the two days.

Katia could grow into a Category 3 hurricane with maximum sustained winds of 115 mph by Saturday afternoon, perhaps more than 500 miles east of Puerto Rico, the hurricane center said. It is too early to predict whether the storm will threaten land.

Category 3 hurricanes have maximum sustained winds of 111 to 130 mph.

Katia is the storm name that replaced Katrina in the revolving list of names, according to the center. The list of Atlantic hurricane names is repeated every seven years and this year the list that was used in 2005 is being reused.

A storm name is retired if it is used for a hurricane that caused major damage, as Katrina did in New Orleans in 2005.

"The only time that there is a change is if a storm is so deadly or costly that the future use of its name on a different storm would be inappropriate for obvious reasons of sensitivity," the hurricane center said.

In its 11 a.m. ET advisory, the hurricane center said Katia has maximum sustained winds of 45 mph. The storm was in the open Atlantic about 630 miles west-southwest of the southernmost of the Cape Verde Islands. It was moving west-northwest at 18 mph. That general motion was expected to continue for the next few days.

[Updated at 5:25 a.m. ET] Tropical Storm Katia barreled across the Atlantic Ocean early Tuesday and is expected to intensify and accelerate, the National Hurricane Center in Miami said.

As of 5 a.m. ET, Katia was about 535 miles (855 kilometers) west-southwest of the southernmost Cape Verde Islands and carried maximum sustained winds of 40 mph (65 kph).