MIAMI (AP) — Tropical Storm Carlotta has formed in the Pacific south of Mexico and is expected to become a hurricane.

Carlotta's maximum sustained winds early Thursday are near 40 mph (65 kph). The U.S. National Hurricane Center in Miami says additional strengthening is forecast and Carlotta is expected to become a hurricane by the time it reaches Mexico's southern coast on Friday.

A hurricane watch is in effect for Mexico's Pacific coast from Barra de Tonala to Punta Maldonado.

The tropical storm is centered about 430 miles (695 kilometers) south-southeast of Puerto Angel, Mexico, and 635 miles (1,025 kilometers) southeast of Acapulco, Mexico. The storm is moving northwest near 10 mph (17 kph).

Tropical storm-force winds are extending outward up to 45 miles (75 kilometers).