(CNN) Hurricane Lane weakened as it chugged toward Hawaii on Thursday, but officials warned residents that the storm was still a significant rainmaker.

More than 19 inches of rain fell on a northeastern section of Hawaii's Big Island during a 24-hour period, the National Weather Service said.

The outer bands of the Category 3 cyclone pummeled Big Island on Thursday, triggering landslides and causing flooding that forced officials to close some roads.

The center of the storm -- which could become the first major cyclone to make landfall in the state in 26 years -- is expected to move very close to the main islands or cross land through Friday, the Central Pacific Hurricane Center said

Hurricane Lane is shown in a satellite image from just after 11 a.m. HT Thursday.

Officials fretted over the potential water impacts from the storm, which was moving at 6 mph.

"Lane, while it has been downgraded, is wide and very moist. And it's going to hang around for a while as it moves, because it is moving slowly," Honolulu Mayor Kirk Caldwell said. "And that is why we are taking so much precaution here."

Tom Travis, administrator of the Hawaii Emergency Agency, said the islands almost certainly will have more water -- rain, surf and surge -- than infrastructure can handle.

It could be so devastating Gov. David Ige has urged residents to set aside two weeks' worth of food and water.

He said Thursday that hurricane winds were expected to plow into the Big Island on Thursday night.

The storm's outer bands brought floodwaters to Hilo on the Big Island. Jonathan T. Correa recorded video using a drone over fields near Hilo Bay.

The storm's center, with maximum sustained winds near 125 mph, was in the Pacific about 190 miles south-southwest of the Big Island town of Kailua-Kona around 11 a.m. HT (5 p.m. ET).

Forecaster Leigh Anne Eaton, from the Honolulu office of the National Weather Service, told reporters that Lane is moving into an area where wind shear will further weaken the storm.

But the storm will still be a major hurricane as the eye passes Hawaii, she said.

Forecasters think the storm will turn west -- away from the islands -- but are uncertain when that will happen.

Rain causes landslides

Landslides are a concern, with 10-30 inches of rain forecast through the weekend -- and slides were already happening on the Big Island as the storm's outer bands hit Thursday morning.

On the Big Island's northern tip, landslides were blocking parts of Route 19, the county civil defense agency said

About 3 to 19.15 inches of rain had already fallen on parts of the Big Island in the period from 9 a.m. Wednesday to 9 a.m. Thursday, the National Weather Service office in Honolulu said.

Buses around Honolulu have been picking up some residents and taking them to shelters. All public schools canceled classes until further notice, and many state employees have been asked to stay home.

Tropical storm force winds (39-73 mph) stretch out to 140 miles, so even if the hurricane doesn't make landfall, it could have widespread impact.

This forecast cone, created 5 p.m. ET Thursday (11 a.m. in Hawaii), shows the probable range of Hurricane Lane's center for five days.

A hurricane warning is in effect for the Big Island as well as Maui County and Oahu -- meaning hurricane conditions are expected there. Kauai and Niihau are under a hurricane watch, meaning hurricane conditions are possible and that winds of at least 39 mph are anticipated in the comings days.

Why is Hurricane Lane so rare?

The Central Pacific gets few hurricanes and tropical storms; the Atlantic or Eastern Pacific usually see many more named storms.

A car is partially submerged in water from Hurricane Lane rainfall on the Big Island on Thursday.

Hawaii is a small target in a vast ocean, and isn't often threatened. Hawaii gets a named storm within 60 miles of its coastline about once every four years on average, forecasters say.

Lane could become a further rarity if its center crosses land. Only two hurricanes have made landfall in Hawaii since the 1950s: Hurricane Dot in 1959, and Hurricane Iniki in 1992.

Maui includes helicopters in emergency plans

Maui County Mayor Alan Arakawa told CNN affiliate KHON that a lot of rain will be "very problematic."

He is worried that if waves reach 20 feet on the south shore of Maui, roadways could be overwhelmed and tens of thousands of people could be cut off from emergency crews.

Workers clean debris from a stream near Honolulu, trying to get ahead of water from the hurricane.

Arakawa said officials are looking at emergency helicopter services in case they need to move people.

"We're going to have to just bear down and wait like everybody else to see what really happens when the storm hits us," he told KHON. "I'm hoping and all us here are praying the storm dissipates and disappears, but from all indications we are going to have heavy flooding and high winds no matter where Lane decides to go."

Authorities are asking people to seek shelter before it's too late or to stay in their homes if they believe those structures can withstand hurricane winds or storm surge.

Many others are leaving. Long lines were seen at airports in Honolulu as hundreds of people tried to catch flights out of the islands before the storm comes closer.

The 15 airports throughout the state will remain open as long they don't suffer damage to their infrastructure or the debris "makes flight operations unsafe," the Hawaii Department of Transportation said in a statement.

Rain, rain, and more rain! Animation of forecast precipitation totals Wed-Sat afternoon. Flooding & landslides a big concern with #HurricaneLane. #HIwx pic.twitter.com/HQCnyBkH40 — NWSHonolulu (@NWSHonolulu) August 23, 2018

The US Coast Guard ordered Honolulu County ports closed Thursday. Hawaii and Maui County ports had already been closed.

President Donald Trump approved a disaster declaration ahead of the storm.

In a statement announcing Trump's approval, Gov. Ige said Hawaii had submitted the request for a Presidential Major Disaster Declaration to help with the impact the hurricane may have in the islands.

Some windows on a home in Milolii, Hawaii, are boarded up as residents await the full brunt of Hurricane Lane.

"The approval of the Presidential Disaster Declaration means that Hawai'i will have quick and efficient access to federal resources in the wake of Hurricane Lane, as our communities and residents recover from any damage and losses caused by the storm. We are grateful to the President and FEMA for the swift approval of our request as our state braces for the severe weather ahead," the governor said.