A tropical depression formed over the southwestern Gulf of Mexico on Sunday and was expected to develop into a tropical storm within 24 hours before moving over eastern Mexico and the city of Veracruz on Monday.
The U.S. National Hurricane Center said Tropical Depression Four was located some 190 miles (305 km) east-southeast of Tuxpan, Mexico, with maximum sustained winds of 35 mph (55 kph).
The Miami-based center said the storm was forecast to strengthen and could become a cyclone at any time before it moved over eastern Mexico. The system would be named Danielle if it reaches sustained tropical storm-force winds of 39 mph (63 kph).
The NHC issued a tropical storm warning for the state of Veracruz. Forecast models showed the storm coming ashore just north of the city of Veracruz, which has more than 400,000 residents.
"Areas of heavy rain are expected over portions of eastern Mexico tonight through Tuesday," the center said. "These rains could cause life-threatening flash floods and mud slides, especially in areas of high terrain," it added in its advisory.