A tropical wave in Caribbean Sea strengthened slightly overnight and extends from eastern Cuba and Jamaica toward Hispaniola and Puerto Rico and north of the sea, according to the 2 p.m. forecast from the National Hurricane Center in Miami.

The center is watching the wave closely because it continues to have the potential to become the first named storm of the Atlantic season. If so, it would become Tropical Storm Alex.

Forecasters maintained again that the system has a 30 percent of becoming a tropical cyclone over the next 48 hours.

"Upper-level winds still appear conducive for some slow development as the system moves westward or west-northwestward around 10 mph over the next day or two," the forecast said. "Heavy rainfall could affect portions of Jamaica, Cuba, Haiti, the Dominican Republic, and Puerto Rico over the next couple of days."

Late Tuesday, forecasters pegged the chances of the storm growing into a named system at 20 percent.

"The storm is now going through a cycle where it is building another respectable mass of heavy thunderstorms, and the increased inflow of low-level air that will feed these thunderstorms will likely enhance . . . [the system's] spin today,"

Jeff Masters of Weather Underwrote wrote on his blog this morning

The wave has some "modest circulation" at high levels but not close to the ground, according to Masters.

Meanwhile in the Pacific, Hurricane Celia has re-strengthened to a Category 2 storm. The hurricane center said Celia's maximum sustained winds increased today to near 100 mph. Some additional strengthening is possible.

The storm is about 740 miles south of the southern tip of Mexico's Baja California peninsula and is heading west — farther out to sea — at about 12 mph.

Additionally, Tropical Storm Darby is gaining strength in the Pacific south of Mexico. Its maximum sustained winds have increased to about 50 mph with additional strengthening forecast.

Darby is south of Salina Cruz, Mexico, moving west-northwest near 9 mph.