MEXICO CITY (AP) — Tropical Storm Boris formed off Mexico's Pacific coast Tuesday and headed for an expected overnight landfall with heavy rains, leading authorities to evacuate seaside and mountain neighborhoods vulnerable to floods and mudslides.

Forecasters predicted torrential rains for the southern coastal states of Chiapas and Oaxaca.

The Chiapas state civil defense office said that it had evacuated about 300 people around the coastal community of Arriaga by Tuesday afternoon and that further evacuations could be made. The state cancelled school in many areas, and mud and rockslides were reported on some state roads.

The U.S. National Hurricane Center in Miami said Boris was centered about 85 miles (140 kilometers) east-southeast of Salina Cruz late Tuesday. It was moving north at about 5 mph (7 kph) and had maximum sustained winds of about 40 mph (65 kph).

The center predicted the storm would begin weakening once ashore and said it probably would dissipate Wednesday night.

Boris could drop as much as 10 inches (25 centimeters) of rain over southern Mexico, creating the risk of deadly floods and mudslides, the center said. Even heavier amounts of rain could be seen in some places, it warned.

A tropical storm warning was in effect in southern Mexico from Salina Cruz to Mexico's border with Guatemala.