HONOLULU -- The Big Island and Maui are under a tropical storm watch as a Category 4 hurricane approaches Hawaii.

The current forecast has Hurricane Ignacio passing northeast of the Big Island on Monday and north of Maui on Tuesday. It's possible that the storm will still be at hurricane strength during that time, the Maui News reported.

Stormy weather could hit the Big Island on Sunday night and Maui on Monday, the Central Pacific Hurricane Center reported.

Hurricane Ignacio is 640 kilometres east of Hilo and has sustained winds of 209 kph, said Anthony Reynes, a meteorologist with the Central Pacific Hurricane Center.

"Right now, the current track, we're not expecting the hurricane to make a direct hit on the Big Island," Reynes said. "Mainly the impacts are going to be very high surf and some strong wind gusts over the coastal waters."

Maui Mayor Alan Arakawa and Hawaii Gov. David Ige have signed emergency proclamations as the islands prepare for high winds, heavy rain and ocean swells.

Honolulu Mayor Kirk Caldwell said at a news conference on Sunday that city officials are preparing to prevent more sewage spills in case the storm touches Oahu, the Honolulu Star-Advertiser reported.

Approximately 3.8 million litres of treated but not yet disinfected wastewater spilled from the East Honolulu Wastewater Treatment plant, closing Sandy Beach and its surroundings Thursday. On Monday, 1.5 million litres of wastewater spilled in Ala Moana Beach Park after heavy rains associated with Tropical Storm Kilo inundated the system.

The cause of the Ala Moana Beach Park spill was traced to city sewer pumping stations that were offline because of construction, the Star-Advertiser reported. Honolulu officials confirmed that all stations are online, and workers have positioned extra pumps in case of flooding.