Oahu felt the worst of the Kona low that brought heavy rain and thunderstorms to Hawaii on Thursday, resulting in road closures and event cancellations, changes and postponements throughout the day.

The island was under a flood advisory much of the day and into the night as heavy showers doused many areas early in the day. Although the downpours eased in the afternoon and evening, elevated streams and saturated ground meant that flooding was still a threat.

Oahu, Niihau, Kauai, Molokai and Lanai remained under a flood watch through this evening. The flood watch for Kahoolawe and Maui was lifted Thursday afternoon.

The National Weather Service said the Kona-­ low system will continue bringing unstable tropical moisture over the islands for the next couple of days before it drifts away from the state.

“We are still expecting additional impacts (Thursday night) through at least late Friday,” forecasters said. “As showers rain over already saturated areas, flash flooding will be possible and streams will become more responsive to downpours.”

Rain gauges recorded over 3 inches of rain in Kaneohe and Maunawili over a 12-hour period Thursday.

City and state road crews were busy Thursday, closing roads and clearing debris across Oahu due to landslides and downed trees.

A fallen tree and landslide closed the right lane of Pali Highway Honolulu-bound at Castle Junction in Kailua in the morning. Later in the day, Kalanianaole Highway’s Kailua-bound lanes before Kapaa Quarry Road were closed due to a “large downed tree,” according to the state Department of Transportation.

DOT crews also responded to downed trees on Likelike Highway Kaneohe-bound before the Wilson Tunnel, and on Kamehameha Highway northbound after Waikalani Drive, according to spokesperson Shelly Kunishige.

Crews responded to flooding on Farrington Highway at Mailiili Road and at Lualualei Naval Road, as well as on Nimitz Highway westbound at River Street.

City Department of Transportation Services crews were also out repairing damaged traffic signals around Oahu on Thursday.

“We just want to remind people that in this kind of weather, give extra caution, pay attention and drive slower and safely,” said DTS spokesperson Travis Ota.

The city Department of Environmental Services responded to a wastewater spill near the intersection of Kaau Street and Palolo Avenue, which was “caused by high flow as a result of sequential storm events with extremely heavy rainfall,” according to a city news release.

About 18,000 gallons of raw wastewater was spilled, with crews recovering 4,000 gallons from the ground. About 14,000 gallons spilled into a nearby storm drain, of which about 6,000 gallons of wastewater mixed with storm water was recovered, officials said.

The state Department of Land and Natural Resources closed the Diamond Head State Monu­- ment on Thursday morning due to heavy rain resulting in heavy runoff and minor rockslides at the tunnel entrance and along the trail, according to a DLNR spokesperson. The Honolulu Zoo also was closed due to flooded walkways, and play at several city golf courses was suspended intermittently throughout the day due to rain.

“The closures are largely made on an as-needed basis, when the volume of rain necessitates closures of certain areas, and closures are always made in the interest of public health and safety,” Ian Scheuring, the mayor’s deputy communications director, said in an email.

All Hawaii High School Athletic Association softball semifinal games scheduled for Thursday at the UH Rainbow Wahine Softball Stadium were postponed until today. Radford High School’s graduation ceremony, scheduled for 6 p.m. today, also was moved from the Tom Moffatt Waikiki Shell to the Neal S. Blaisdell Arena “due to impacts from severe weather,” according city officials.

On Wednesday night the Honolulu Department of Emergency Management partially activated its Emergency Operations Center. It is expected to remain activated until at least today.

“During activations like this one, the Department of Emergency Management coordinates emergency response by all of our first responder agencies, as well as the departments that manage public works,” Scheuring said. “All of these agencies have representatives present in the EOC so that they can coordinate as needed.”

Gov. Josh Green also signed an emergency proclamation in response to the Kona-low weather event Wednesday night. The proclamation allows the adjutant general to activate units of the National Guard to work with local authorities, emergency management agencies and other organizations to mitigate any storm impacts.

National Weather Service meteorologist Thomas Vaughan said the state likely will see increased rainfall at least through Saturday.

“Based on the latest models, we could see some enhanced rainfall especially over Kauai into Saturday for sure. Elsewhere, by late Saturday, we’ll probably see some significant improvements for the remaining islands,” he said. “By Sunday, things look … like things should be winding down, and then by Monday, we should be back to a much-drier pattern.”