Map: Tracking Tropical Storm Lidia

Lidia was a tropical storm in the North Pacific Ocean Tuesday morning Pacific time, the National Hurricane Center said in its latest advisory.

The tropical storm had sustained wind speeds of 40 miles per hour.

Tropical-storm-force winds, with sustained speeds of at least 39 miles per hour, typically arrive as weather conditions begin to deteriorate, and experts say their estimated arrival time is a good deadline for completing storm preparations and evacuating if asked to do so.

Lidia is the 12th named storm to form in the Eastern Pacific in 2023.

Whether a storm forms in the Atlantic or the Pacific, it generally moves west, meaning Atlantic storms pose a greater threat to North America. If a storm forms in the Pacific close to land, it can bring damaging winds and rain before pushing out to sea.

However, an air mass can sometimes block a storm, driving it north or northeast toward the Baja California peninsula and the west coast of Mexico. Occasionally, a storm can move farther north, as the post-tropical cyclone Kay did last year, bringing damaging wind and intense rain to Southern California. Some storms even move across states: In 1997, Hurricane Nora made landfall in Baja California before moving inland and reaching Arizona as a tropical storm.

Hurricane season in the eastern Pacific began on May 15, two weeks before the Atlantic season started. Both seasons run until Nov. 30.

Complicating things in the Pacific this year is the likely development of El Niño, the intermittent, large-scale weather pattern that can have wide-ranging effects on weather around the world.

In the Pacific, El Niño reduces wind shear, or changes in wind speed and direction. Those changes normally help prevent the formation of storms, so a reduction in wind shear increases the chances for storms. (In the Atlantic, El Niño has the opposite effect, increasing wind shear and thus reducing the chances for storm formation.)