An area of low pressure in the Atlantic had a 90 percent chance on Sunday evening of developing into a cyclone in the next two days.
The weather pattern was causing showers and thunderstorms in an area near the Lower Antilles, an 8 p.m. NOAA bulletin said.
It was moving west-northwest at around 15 mph Sunday evening. If it became a storm, Puerto Rico and the Lower Antilles might be in its path.
Meanwhile, Tropical Storm Eugene in the Pacific Ocean has a high chance of strengthening into a hurricane in the next 48 hours, according to an NOAA advisory.
Eugene could become a hurricane by late Tuesday.
The storm was about 415 miles south of Acapulco Sunday. Winds reached 45 miles per hour.