Felicia’s winds diminished slightly overnight but the tropical storm maintained a course that would start hitting the eastern Hawaiian islands tonight.

The Big Island, Maui County and Oahu are all under a tropical storm watch. The Central Pacific Hurricane Center said this morning that if expected weakening of Felicia to a tropical depression later today does not occur, some of those islands will be placed on a tropical storm warning by tonight.

Felicia, once a powerful category 4 hurricane, now has 45 mph maximum sustained winds with higher gusts and is moving west at 12 mph. As of 5 a.m. today, it was about 325 miles east of Hilo and about 500 miles east of Honolulu. Tropical storm force winds of 39 mph or more extend up to 125 miles from the center, forecasters said.

“Regardless of the strength of Felicia when it reaches the Hawaiian islands, heavy rains are still expected to occur and flash flooding remains a possibility,” the hurricane center said.

The latest track shows Felicia traveling north of the Big Island as a tropical depression tonight and just south of Oahu later Tuesday.

A swell generated by Felicia has already hit the main Hawaiian islands.

A tropical storm watch means tropical storm conditions are possible in the watch area within 48 hours.

Rainfall and the areas affected are dependent on the track Felicia takes, a weather service report said.

A flash flood watch is in effect for Kahoolawe, Lanai, Maui, Molokai, and the Big Island through Tuesday afternoon.

“Felicia is expected to produce extremely heavy rainfall with the potential for widespread flash flooding, increasing on Tuesday and continuing into Wednesday,” forecasters said.

People in flood-prone areas need to prepare for the possibility of torrential rains and rock and mudslides. Flooding rainfall could occur well away from the center of Felicia.

A high surf warning is in effect for Maui and the Big Island until Tuesday night. The surf will likely exceed the warning level of 15 feet. Oahu, Kauai and Niihau are under high surf advisory until Wednesday evening.

Public schools remain open today, the Department of Education Web site said. One charter school, West Hawaii Explorations Academy on the Big Island, will be closed.

Felicia peaked as a category 4 hurricane with winds topping 140 mph on Thursday when it was still in the Eastern Pacific.