People on Hawaii’s Big Island were bracing for another potentially catastrophic storm Friday as Hurricane Nolo churned south of the islands, threatening to unleash flash floods, powerful winds and dangerous surf through the weekend.

Nolo’s maximum sustained winds increased to 105 mph (165 kph) Friday, with the storm expected to strengthen into a major hurricane Saturday. Its center was about 145 miles (235 kilometers) south of Hawaii’s southernmost point.

Forecasters warned that parts of the Big Island could receive up to 15 inches (38 centimeters) of rain, with isolated totals reaching 25 inches (64 centimeters). The forecast was revised downward from an earlier projection of as much as 35 inches (89 centimeters).

Michael Brennan, director of the National Hurricane Center, urged residents to remain indoors and in safe locations as the storm approaches.

"People are going to want to kind of shelter in place on the Big Island, be in their safe place, certainly by later today, tonight, well into Saturday,” Brennan said Friday. "Don’t venture out if you don’t have to into the dangerous flooding environment, but also high winds. We can have trees and power lines down.”

The hurricane center also warned that heavy rainfall could affect Hawaii’s other islands. Maui faced the threat of intense rain, potentially life-threatening flooding and mudslides, forecasters said.

Crews on the Big Island spent hours Friday trying to build berms to guide water and move large debris ahead of the worst of the rain, said Erika Kapu, Hawaii program manager for the humanitarian nonprofit CORE.

CORE and other nonprofit partners spent the week packing and shipping supplies such as camp stoves and hygiene products by air cargo from Oahu to the Big Island for a community relief hub that has been active since August’s Hurricane Lala.

President Donald Trump on Friday approved an emergency declaration for the state of Hawaii, authorizing the Federal Emergency Management Agency to coordinate assistance from across the federal government and provide funding support for emergency measures.

Hawaii officials told residents to put together emergency kits, and the governor issued an emergency proclamation, activating more than 230 Hawaii National Guard members. Schools were closed in some areas.

Hawaii County officials on the Big Island urged residents in flood-prone areas to consider taking refuge at shelters being set up or other locations.

The heaviest rain from Nolo was likely to fall over the same southeastern region of the Big Island that was hit by Lala and where the ground remained wet from additional precipitation. The storm surge could reach 1 to 3 feet (30 to 91 centimeters), creating large and dangerous waves and coastal flooding, the hurricane center said.

Hawaiian Electric, the state’s primary utility, said crews that had been helping restore power in Kauai after this month’s Hurricane Lowell would return to Oahu, Maui and the Big Island in preparation for the coming storm.

Residents and tourists on the Big Island were busy preparing.

In Hilo, where light rain was falling Friday, residents filled bags with sand and gravel at Francis Wong Stadium, where authorities had set up a sand distribution center.

Dean Taise said water was starting to get into his driveway from the street, so he decided to get a few sandbags ready ahead of possible flooding.

"They say, prepare for the worst, right? Hope for the best,” Taise said.

Piles of sandbags lined the terminal at Hilo International Airport, where Daniela Mendoza was trying to get home to Oahu after Southwest Airlines canceled flights. Only Hawaiian Airlines was still flying out of the airport Friday afternoon.

"I hope I can leave,” Mendoza said. "My cats are waiting for me.”

Meanwhile, Mexico was under threat from Hurricane Polo as it headed toward the Baja California peninsula after bringing storm conditions to the southwestern coast.

The hurricane center said Polo gained significant strength overnight into Friday morning and doused parts of Mexico’s Pacific coast. No major damage or flooding was reported along the coast overnight into Friday.

By midday Friday, attention had turned to the peninsula, where the hurricane was expected to turn back and make landfall between Monday and Tuesday. Local authorities were preparing shelters, and Mexico’s government announced Friday afternoon that it was closing ports in the region as dark clouds swirled overhead.

The latest estimated sustained winds were 175 mph (280 kph).

Residents stacked sandbags to fortify beachfront shops and evacuated their homes in some coastal areas Thursday. Mexican authorities opened shelters and cleared people from beaches, and 15,000 security personnel were deployed across the coast. Schools were closed.

In the port city of Lázaro Cárdenas in Michoacán, seawater swept through homes, leaving wooden planks and furniture strewn across the streets. Residents and government officials were clearing debris and shoveling thick mud that coated much of the town.

Alicia Contreras said the walls and roof of her restaurant had been severely damaged by 15-foot (4.5-meter) waves. She worried about how she would recover financially, saying she has no other source of income.

Brennan said some moisture associated with Polo would be pushed into parts of the southwestern U.S. by Monday, possibly producing scattered flash flooding in the Four Corners region, particularly in parts of Arizona and New Mexico.

Biologists on Friday relocated eggs from two olive ridley sea turtle nests on Southern California beaches to the Aquarium of the Pacific in Long Beach over concerns about high tides and hazardous surf as officials monitored Hurricane Polo.

El Niño is prompting major environmental shifts across the world, fueling drought in some areas and flooding in others. It traditionally dampens the Atlantic hurricane season, while it tends to increase tropical cyclone activity in the Pacific because of moist air and low wind shear.

A third storm in the Pacific, Hurricane Odalys, was at Category 4 status and remained far from land Friday, roughly 955 miles (1,537 kilometers) west-southwest of the southern tip of the Baja California peninsula.

Two other powerful storms were churning in the Atlantic Ocean but were not near land.

In the northern Atlantic, Tropical Storm Fay reformed early Thursday. As of Friday, it was about 1,040 miles (1,674 kilometers) west-southwest of the Azores, the hurricane center said. Off Africa’s western coast, Tropical Storm Gonzalo strengthened early Friday as it approached the Cabo Verde Islands.