Tropical Storm Lala strengthened Friday and is expected to reach the Big Island today as a Category 1 hurricane.

At 5 p.m. Friday, Lala had 65mph maximum sustained winds and was located about 235 miles east-southeast of South Point and was moving west-northwest at 12 mph, according to the Central Pacific Hurricane Center.

A hurricane warning is in effect, and tropical-storm-force winds extend outward up to 220 miles from the center.

The forecasts underscore the potential for dangerous conditions today on the Big Island.

In the Kona area, peak winds are forecast at 55 mph to 70 mph, with gusts up to 85 mph, while parts of the Big Island’s southern and southeastern areas face similar potential for hurricane-force winds.

Heavy rainfall is also forecast, with 8 to 12 inches expected across the Big Island and localized totals of up to 25 inches.

High surf warnings remained active for east-facing shores of the Big Island, where surf is projected today to reach 15 to 20 feet and 10 to 15 feet, respectively.

Forecasters warn that Lala’s swells will spread westward across the state, producing life-threatening surf and rip currents.

Very large and extremely rough seas are expected to increase rapidly today and Sunday, with the potential for damaging surf, beach erosion and overwash of vulnerable coastal infrastructure, particularly on the Big Island.

Gov. Josh Green, in a press conference early Friday evening in Honolulu, to urged people to stay sheltered and off the streets during the storm.

“Suffice it to say, it’s not just the amount of wind — it’s the heavy rainfall, it’s the flooding, it’s the entirety of this storm which gives us pause,” Green told reporters. “This is a very serious storm. We have not had a hurricane make landfall in quite some time, so none of us have really experienced this in the last couple of decades.”

The last hurricane to make landfall in Hawaii was Hurricane Iniki in 1992, which caused severe damage on Kauai.

Hawaiian Electric Co. warned utility customers across the state Friday to prepare for power outages that could last for days in the wake of Lala.

Lala’s heavy rains and winds could topple trees, especially albizias which have shallow root systems and can grow as tall as 100 feet. Albizias can cause significant damage to power lines if they fall.

Hawaiian Electric also said its customers should avoid any downed power lines. Electrical wires might remain charged when they land on the ground. The utility said that more than 500 workers are ready to restore power.

In March, a Kona low storm knocked out power to tens of thousands of customers, hundreds for as long as a week, when a low-pressure system blew across the state, said Jim Kelly, a spokesperson for the utility.

He said the power company has worked to harden its grid against severe weather and other conditions, but some equipment remains vulnerable to downed trees and windblown debris.

“This is expected to be one of the most dangerous and damaging storms we’ve experienced in a long time,” Kelly said.

He said the storm could bring the most devastation to the state since 2014, when Tropical Storm Iselle caused widespread damage that required months of recovery.

All Hawaii County and solid waste facilities are closed today, and all Hele-On bus routes and Paratransit services are cancelled today and Sunday.

The county on Friday urged residents to complete their preparations and plan for sheltering and staying off roadways during the storm.

“With this storm we are facing a significant risk of damaging winds and flash flooding, and we encourage all of our residents and visitors to prioritize their safety,” Mayor Kimo Alameda said Friday morning in a statement. “Complete your storm preparations … including securing your home, ensure you have access to safe shelter, and check on neighbors who may need assistance.”

Alameda also signed an emergency proclamation Friday morning, which allows the county to streamline its response and coordinate resources. Gov. Josh Green signed an emergency proclamation for the state on Thursday.

The county at 6 p.m. Friday opened emergency shelters islandwide. They are:

• Hisaoka Gym in North Kohala

• Waikoloa Elementary School Cafeteria, Waikoloa Village

• Kahilu Town Hall, Waimea

• Honokaa Armory, Honokaa

• Laupahoehoe Charter School Band Room, Laupahoehoe

• Waiakea High School Gymnasium, Hilo

• Keaau Armory, Keaau

• Pahoa Community Center, Pahoa

• Pahala Gymnasium, Pahala

• Naalehu Elementary School Gymnasium, Naalehu

• Yano Hall, Captain Cook

• Kealakehe High School Gymnasium, Kailua-Kona

Anyone using the shelters should bring their own personal and sleeping supplies, officials said. All the shelters are pet-friendly, the county said, but animals must be in a carrier.

The New York Times contributed to this report.