MIAMI (Reuters) - The 15th tropical storm of a busy Atlantic hurricane season developed in the Caribbean on Tuesday while a 16th tropical system began to form off Central America and former Tropical Storm Nana unravelled and disappeared.
The new storm, Omar, was expected to bring heavy rains to Puerto Rico and the Virgin Islands and could be near hurricane strength, with winds of at least 74 miles per hour (119 km per hour), when it skirts the eastern shores of Puerto Rico on Wednesday, the U.S. National Hurricane Centre said.
Storm alerts were posted for Puerto Rico, the U.S. Virgin Islands, the British Virgin Islands and the eastern portion of the Dominican Republic as Omar swirled around 355 miles (570 km) south-southwest of San Juan, the Miami-based centre said.
The storm was drifting towards the east-southeast and was expected to gradually turn to the northeast. Its top sustained winds by late Tuesday morning had reached 40 mph (65 kph).
While Omar menaced Puerto Rico, a new tropical depression developed just off Honduras.
The 16th depression of the season, which would be called Paloma if it strengthened into a tropical storm, was expected to come ashore somewhere between eastern Honduras and Belize.
Its eventual strength would depend on how much time it spent over warm Caribbean waters.
The hurricane centre's official forecast did not foresee the system becoming a hurricane before landfall and it did not appear to present a threat to the U.S. mainland or to the oil fields of the Gulf of Mexico.
Former Tropical Storm Nana, which developed on Sunday midway between the Cape Verde Islands off Africa and the Caribbean, dissipated on Tuesday after being torn apart by atmospheric winds.
The 2008 hurricane season has been busy and has six more weeks to go before it officially ends on November 30. An average season spawns 10 storms, of which six strengthen into hurricanes.
So far this year, Hurricane Gustav slammed ashore near New Orleans, the city devastated by Hurricane Katrina in 2005, and Hurricane Ike hit Houston. Both threatened the oil rigs off the U.S. Gulf Coast that supply a quarter of U.S. domestic oil.
In Haiti, more than 800 people were killed after the impoverished Caribbean nation was swamped by Fay, Gustav, Hanna and Ike, and Cuba suffered $5 billion in damages after being raked by Gustav and Ike.
(Reporting by Michael Christie; editing by Jim Loney and Mohammad Zargham)