Hurricane Madeline rapidly intensified into a major Category 3 storm Monday as it churned relentlessly westward toward the Hawaiian Islands.

Its track raised the possibility of a brush as early as Wednesday with the Big Island, where a hurricane watch went into effect at 11 a.m. Monday.

A second, even stronger storm, Hurricane Lester, followed in Madeline’s wake.

At 8 p.m. Madeline, packing 125 mph winds, was about 550 miles east of Hilo and traveling west-northwest at 10 mph, according to the Central Pacific Hurricane Center. That put it just over two days away from possible landfall if the course and speed hold.

At 5 p.m. Monday Lester, a Category 4 hurricane with sustained winds of 140 mph, was 1,525 miles east of Hilo and traveling west at 15 mph, according to the National Hurricane Center.

“Whether it’s a tropical storm or a hurricane, any of those systems can do damage,” said National Weather Service meteorologist Eric Lau. “The main message is to have people be prepared.”

Winds of 110 mph can damage well-built framed houses, remove roof decking, snap trees and cause blackouts, Lau said, adding, “We don’t want people to take it lightly.”

Madeline will also likely bring heavy rain Wednesday to Hawaii County, with up to 15 inches in some areas, with possible flash flooding and mudslides, the weather service said.

Surf of up to 25 feet could hit the east shores of Hawaii island today and Wednesday, possibly damaging coastlines.

The weather service issued a high-surf warning for east-facing shores of the other islands through 6 a.m. Thursday, with waves up to 20 feet expected.

Lester also gained strength Monday but was forecast to lose some punch before getting here.

Meanwhile the Hawaii Emergency Management Agency canceled the monthly siren test scheduled for 11:45 a.m. Thursday, saying that blaring sirens might confuse the public.

The weather service emphasized that the public should not focus on the exact forecast track, because storms can suddenly change course.

The hurricane center recommends securing loose outdoor objects, which could become destructive projectiles, and protecting windows with plywood.

Hawaii County Civil Defense recommended that residents prepare for water and power outages and to put together a several-day supply of nonperishable food, flashlights, batteries, cash and medication, and to keep vehicles fueled and cellphones charged.