HOUSTON — Hurricane Melissa strengthened into a major Category 4 hurricane, with the possibility of intensifying to a Category 5 storm Sunday night, unleashing torrential rain and threatening to cause catastrophic flooding in the northern Caribbean, including Haiti and Jamaica, the U.S. National Hurricane Center said.

The storm is expected to hit Jamaica, Haiti and the Dominican Republic, as well as Cuba, the Bahamas, and the Turks and Caicos.

At 8 a.m. Saturday, the National Hurricane Center issued an advisory stating that Tropical Storm Melissa is in the Caribbean Sea, 160 miles southeast of Kingston Jamaica and 235 miles southwest of Port Au Prince Haiti. The system, with maximum sustained winds of 70 mph, is moving west-northwest at 1 mph.

Melissa is currently the only active tropical system in the Atlantic basin. As of Friday night, the storm remains nearly stationary, drifting north at just 2 mph. Maximum sustained winds are around 65 mph—just below the 75 mph threshold needed to reach Category 1 hurricane status.

Tropical Storm Sonia is churning in the Pacific Ocean and isn’t threatening land. The U.S. National Hurricane Center says the storm formed over the weekend and on Monday was about 965 miles southwest of the southern tip of Mexico’s Baja California peninsula.