MIAMI -- Sandra has weakened to a tropical storm as it approaches Mexico's Pacific coast.

The storm's maximum sustained winds decreased Friday evening to 70 mph (115 kph). The U.S. National Hurricane Center says Sandra is forecast to continue weakening and is expected to be near tropical storm strength as it approaches the Mexican coast on Saturday.

Sandra is centred about 150 miles (240 kilometres) southwest of Las Islas Marias, Mexico, and is moving north at 10 mph (17 kph).

A tropical storm warning is in effect for Las Islas Marias and for the area from Altata to San Blas.