MIAMI — Tropical Storm Dalila is churning across the Pacific off southwest Mexico, and authorities have issued a tropical storm warning for a large swath of coastline.

The U.S. National Hurricane Center in Miami said the fourth tropical storm of the season formed early Sunday and is centered about 235 miles (375 kilometers) south-southeast of Manzanillo, Mexico. Dalila is moving north-northwest at 9 mph (15 kph), with top sustained winds of 40 mph (65 kph).

Mexico has issued a tropical storm warning for its Pacific coast from Punta San Telmo to La Fortuna. A tropical storm watch is issued from north of La Fortuna to Cabo Corrientes.

Forecasters say Dalila is showing little change in strength. Tropical storm conditions are expected to reach the coast early Monday with 1 to 3 inches of rain in some areas.