Tropical Storm Priscilla forms in the Pacific. Maps show its path.

Tropical Storm Priscilla formed Saturday off the west coast of Mexico, where it was forecast to bring dangerous surf and possible flooding, the National Hurricane Center said.

Priscilla strengthened Sunday morning as it moved over Pacific waters on a path expected to run parallel to the land, with tropical storm watches in effect for a vast stretch of the Mexican coastline from the southwestern state of Jalisco up to the Baja California peninsula. 

Forecasters issue a tropical storm watch for a particular area when tropical storm conditions are possible in that area, typically within 48 hours of the watch being issued, according to the hurricane center.

On its forecast track, Priscilla’s center was expected to remain offshore of the southwestern Mexican coast and travel parallel to the land through the early part of the week, the center said.

Forecasters said in an advisory early Sunday that Priscilla would likely develop into a hurricane by the end of the day and could continue to strengthen for another day after that. 

At around 7 a.m. ET, the storm was located about 295 miles south-southwest of Cabo Corrientes, near the resort town Puerto Vallarta, and about 495 miles south-southeast of the southern tip of Baja California, according to the advisory. It was traveling north-northwestward at 5 mph with maximum sustained winds of 65 mph — roughly 10 mph below the minimum threshold for a storm to be considered a hurricane. 

Although Priscilla was not forecast to directly touch land, the hurricane center said tropical storm conditions, including powerful winds, were possible in areas under a tropical storm watch on Sunday and Monday. 

Heavy rain, and, possibly, flash flooding, was also expected across parts of southwestern Mexico through Monday.

“Across coastal portions of Michoacán and far western Guerrero, rainfall amounts of 4 to 6 inches are expected, with local amounts of up to 8 inches,” the hurricane center said in its advisory. “Across Colima, western Jalisco, and the rest of Guerrero along the coast, 2 to 4 inches of rain are expected. This rainfall will bring a risk of flash flooding, especially in areas of higher terrain.”

Priscilla could also generate potentially life-threatening surf conditions and rip currents in coastal areas of southwestern Mexico and the Baja California peninsula, the hurricane center said. Some areas were already beginning to feel those effects Sunday, but forecasters warned that they may become more widespread by Monday.