MEXICO CITY, June 12 (Reuters) - Tropical storm Calvin formed off Mexico's Pacific coast on Monday, bearing down on the southern states of Chiapas, Oaxaca and Guerrero where it could dump as much as 20 inches (51 cm) of rain, the U.S. National Hurricane Center (NHC) said.
On Monday afternoon, Calvin was about 70 miles (113 km) east-southeast of the coastal town of Puerto Angel in southern Mexico, according to the Miami-based NHC. The storm was blowing maximum sustained winds of 40 miles per hour (64 kph), and moving west-northwest at 2 miles per hour, the NHC added.
"On the forecast track, the center will be near or over the coast tonight or early Tuesday," the NHC said. "Little change in strength is expected until landfall, and weakening will occur after the center moves inland."
The storm is projected to rain 5-10 inches, but there could be isolated downpours of up to 20 inches, the NHC said. The rains could well result in "life-threatening flash floods and mudslides," the NHC said.
State-owned oil company Pemex's Salina Cruz refinery is in Oaxaca. (Reporting by Gabriel Stargardter; editing by Grant McCool)