Monday’s powerful kona low weather system knocked out power to hundreds of downtown Honolulu and Chinatown businesses, government buildings and residents at night, and Hawaiian Electric was warning customers to plan for an extended outage.

The utility’s Iwilei substation was flooded and crews were on the scene, but officials with the company said it will be unlikely they can pump out the facility until the rain stops.

Officials said power wasn’t likely to return until this morning at the earliest.

The affected area is bounded roughly by South Beretania Street, River Street, Ala Moana Boulevard and Punchbowl Street. It includes the state Capitol, federal courthouse, state office buildings, office towers on Bishop and Alakea streets and residential condominiums and apartments.

Hawaiian Electric said crews will have to pump out the substation before assessing the damage and attempting to repair the equipment.

The heavy rains and flooding caused at least three transformers to fail Monday night.

“We understand the inconvenience that this causes for our customers and we are committed to restoring power as safely and as quickly as possible,” said Jim Alberts, senior vice president of operations.

However, it is uncertain when the rain will let up because Oahu and Kauai were expected to be pounded by heavy rain and possible thunderstorms again today.

Meanwhile, drier conditions are expected to return to the rain-soaked eastern half of the state.

The weather system caused flooding, power outages and property damage across the islands, prompting Gov. David Ige on Monday to sign an emergency declaration giving him authority to provide financial relief for losses due to the storm.

Oahu experienced the brunt of the slow-moving storm on Monday with radar at 7 p.m. showing most of the island getting rain at the rate of 1 inch to 2 inches per hour and a large patch of rain expected to move over Oahu from the south overnight at rates up to 3 inches per hour.

Earlier in the day, many areas of Oahu showed rainfall totals of 2 to 3 inches over a 24-hour period, the National Weather Service said. In addition, the U.S. Geological Service gauge at Makaha Stream recorded 5 inches of rain in 24 hours, while Poamoho saw over 6 inches.

A busy day for Oahu first responders included the rescue of five boys who had been swept into the rushing waters of Palolo Stream, where they went to play after school.

At about 2:30 p.m. Honolulu Fire Department personnel set up a staging area in the stream behind Jarrett Middle School and rescued the first boy, who let go of the branch he was clinging to as HFD crews pulled him from the water.

A second boy was rescued downstream with the help of a ladder from Engine 33, according to HFD, while crews from Engine 5 found the other three boys, jumped in the rushing water and pulled each one out.

All five boys, ages 9 to 10, were taken to HFD’s Palolo Station for medical evaluation, but they were uninjured and their parents took them home.

Forecasters said Kauai and Oahu will be lashed by rain again today as deep tropical moisture continues to move in from the south, creating the real potential for catastrophic flooding.

Officials warned of possible dangerous driving conditions from near-zero visibility and said some roads could become impassable from runoff and flooding. Landslides will be a continuing threat, they said, while debris in streams and gulches could clog bridges and culverts to unleash dangerous flooding.

As heavy rain and wind battered Oahu on Monday, Honolulu city officials were urging Oahu residents to limit nonessential activities through this morning to avoid flooded areas.

“(There’s) potential for additional heavy rains to start flooding the urban Honolulu area as well as as well as other parts of the island,” Department of Emergency Management Director Hiro Toiya said at a news conference.

The city opened four shelters at Kalakaua District Park, Makaha Community Park, Sunset Beach Recreation Center and Kailua District Park. Toiya said the locations were selected because of the areas’ potential for weather impact and because they can accommodate those who live in harder-to-reach areas that might be cut off from resources.

There were about 19 people at shelters Monday afternoon, and Toiya said more shelters will be opened if necessary.

On Monday night, the state Department of Education announced that all public schools are expected to be open today, with the exception of Pearl City Highlands Elementary and Farrington High, which will be closed due to flooding.

Since 8 p.m. Sunday, the Honolulu Fire Department responded to at least 47 storm-related events that included blown roofs, fallen trees and roadway obstructions.

Honolulu Emergency Medical Services Director Jim Ireland said that while Ocean Safety personnel were busy rescuing people on Sunday due to high surf, fewer people were seen at Oahu’s beaches Monday.

“It’s not a good day to enjoy the outdoors here because of number one, the weather,” he said. “Number two, you’re going to be tying up rescuers if you get into trouble that are potentially needed elsewhere.”

Since last week, Department of Facilities Maintenance employees have been clearing stream mouths to help prevent flooding. However, due to the high surf, some of that work was undone.

“They continue to take action this morning and throughout the day today to the extent that they can,” Toiya said Monday afternoon.

City officials said there will be opportunities for the public to report damage once the storm has passed. The city also will use information from dispatch centers of where responses took place to figure out where the greatest concentration of damage occurred.

The city on Monday also closed the Honolulu Zoo and all six of its golf courses. Scheduled tee times were canceled, and officials said the closures could continue today.

Mayor Rick Blangiardi urged residents to take the weather event seriously.

“We just ask everybody to use caution and common sense,” he said. “Let’s not let the storm get the best of us.”

The weather also affected air travel. On Sunday night, an Amazon cargo container at Daniel K. Inouye International Airport hit two Mokulele Airlines jets, grounding both aircraft. Mokulele is the only passenger carrier that flies to Molokai and Lanai.

“This occurring at the same time as the weather delays that have occurred over the last couple of days, really kind of created a perfect storm,” said Stan Little, chairman and CEO of Southern Airways/Mokulele Airlines.

Normally, planes would just be swapped out, because the airline only flies 10 of its 14 planes in Hawaii at the same time, but the severe weather delayed maintenance for planes.

“We’re working right now on getting planes out of maintenance as quickly as we safely and legally can,” Little said.

Mokulele is currently flying at about 80% of its schedule, and expects to be back at full service by the end of the week, he said.

Kahului Airport lost power Sunday, and due to a mechanical glitch in the generator, was left without power for about three hours. The closure affected two flights — one was canceled and the other diverted to Honolulu until Kahului regained power.

The airport ran off generator power all day Monday and was scheduled to rejoin the power grid at midnight.

A Department of Transportation spokesperson said that while it would have been possible to put the airport back on the main power grid and off the generator sooner, they did not want to compromise any flights during the switch. So out of an abundance of caution, the plan was to wait for a lull in airplane service to make the transition.

Weather officials said winds might not be as big a concern today, because a wind advisory was canceled Monday for the entire state with the exception of the Hawaii island summits. However, there is still potential for some gusts, especially on Kauai.

The winter weather advisory for Hawaii island summits was also canceled Monday due to drier air moving in at the upper levels of the atmosphere, forecasters said.

More typical tradewind weather is expected to reappear on Oahu starting late Wednesday as a drier air mass moves in from the east, they said.

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Star-Advertiser staff writer Peter Boylan contributed to this report.