MIAMI (Reuters) - Tropical Storm Henri formed in the Atlantic Ocean, east of the Caribbean's Leeward Islands, on Tuesday, but was expected to dissipate within two days, the U.S. National Hurricane Center said.

The eighth tropical storm of the 2009 Atlantic hurricane season had sustained winds of 40 miles per hour (65 km per hour) and was located about 600 miles east of the northern Leewards at 5 p.m. EDT (2100 GMT), the hurricane center said.

The system was moving to the west-northwest at 18 mph on a path that would keep it well north of the Caribbean islands in the near future, the center added.

Henri was moving through an area with high wind shear, forecasters said. Wind shear is a difference in wind speeds at different altitudes that can tear apart nascent cyclones.

"The cyclone is expected to weaken to a depression over the next 24 hours and most of the global model fields show Henri dissipating by 48 hours," the hurricane center said in a statement.

Computer models disagreed on the future for the remnants of the cyclone. Several took it to the southwest in the direction of Puerto Rico and Hispaniola, the island shared by Haiti and the Dominican Republic. One had it headed out into the open Atlantic.