Eight feet in 1-1/2 hours.
That is how quickly Kaukonahua Stream rose to flood stage Saturday afternoon, causing the Honolulu Department of Emergency Management to evacuate roughly 80 residents from Otake Camp in Waialua on Oahu’s North Shore.
The speed and intensity of the deluge underscored the importance of heeding flash flood warnings, which were issued for Oahu and Kauai Saturday, with a couple of spots on Oahu receiving 20 or more inches of rainfall in a 24-hour period.
Maui County was under a flash flood advisory briefly from 6 to 9 p.m. Saturday, while Kauai, Oahu and Niihau remained under flash flood watches from 4 p.m. to this morning.
Oahu seemed to get the brunt of the passing weather system, while Kauai’s flash flood warning was canceled at midday.
The Honolulu Department of Emergency Management had issued alerts beginning at 3:37 a.m. Saturday warning that “dangerous flash flooding” was imminent or already occurring.
Unsettled weather from an upper-level trough responsible for the heavy downpours was expected to improve today, according to the National Weather Service. However, another upper-level trough was forecast to move in tonight from the west, bringing more heavy rain and locally breezy tradewinds.
At 5 p.m. Saturday, 24-hour rain gauge totals at two Windward Oahu spots topped the others by far, with the Luluku gauge in Kaneohe receiving 24 inches and the Moanalua gauge on the windward side of the Koolau Range collecting 20 inches of precipitation. The gauge at Poamoho in Waialua measured 17.66 inches.
“These storms were traveling along the spine of the Koolaus, and this particular area (Luluku) got multiple cells or events of very heavy rainfall repeatedly over the same area,” said NWS forecaster Stephen Parker.
He explained that easterly winds force air up over the mountain range to the windward side, helping to “squeeze more rain out of the clouds.”
“These really strong cells were sitting almost still, and that’s what led to these high rainfall amounts,” Parker said, adding that “somewhere between gauges there is going to be a bigger amount.”
Parker said the Luluku gauge is in the area where the state Department of Transportation and police shut down the Likelike Highway off-ramp from the Kaneohe-bound lanes of the H-3 for several hours. A Honolulu Police Department spokesperson said the Likelike closure was the only major one on Oahu Saturday. There were other minor road closures due to flooding, including one in Haleiwa late in the afternoon.
Honolulu firefighters responded to nine water evacuations, including six in Kaneohe, two in Haleiwa and one in Hauula. Meanwhile, Honolulu Fire Department personnel were dispatched to respond to reports of downed trees in Kailua and Kaneohe.
Honolulu Emergency Medical Services’ Crisis Outreach Response and Engagement teams were mobilized to assist a dozen homeless individuals, offering shelter assistance, providing on-scene wound care and handing out blankets and bandages to those in need during the heavy rains.
Videos posted on social media showed chocolate-brown floodwaters flowing behind Hoomaluhia Botanical Garden, kids jumping into a flooded basement-level garage as if it were a swimming pool, motorists braving a torrent of runoff on Kamehameha Highway in Kualoa, and parked cars on a Kalihi street facing inundation.
Another social media video showed two men atop a pickup truck at a Pearl City junkyard trying to prevent floodwaters from flipping the vehicle over and causing it to float away.
Kaukonahua Stream in Waialua rose dramatically to 29.09 feet from 21.3 feet at 12:40 p.m. Saturday, and a good 10 feet higher than earlier in the week, NWS data shows.
The city shut down the Honolulu Zoo, Hoomaluhia Botanical Garden, the ballfields at Patsy T. Mink Central Oahu Regional Park, the Pali Golf Course and Hanauma Bay due to brown water.
First responders notified residents of Otake Camp along Kaupe Road in Waialua to evacuate early Saturday afternoon. Text and email messages from the Department of Emergency Management went out at 12:35 p.m. saying, “FLASH FLOODING in Otake Camp — Waialua.”
The email warned residents in the evacuation area to “LEAVE NOW,” as floodwaters “can move swiftly and rise rapidly. Driving into flooded areas is extremely dangerous and may result in injury or death.”
The city opened shelters for Otake Camp residents, who were given the all-clear at 4:30 p.m. to return to their homes after weather conditions had improved and confirmation that flooding risks had subsided. The shelter at Waialua High and Intermediate School was closed at that same time.
“We appreciate the community’s cooperation and patience as we worked to ensure everyone’s safety,” Mayor Rick Blangiardi said in a written statement. “Our first responsibility is protecting lives, and I want to thank our first responders and emergency personnel for their quick actions and professionalism in helping residents evacuate safely.
“We also thank residents for acting quickly and following evacuation instructions. Because of that cooperation and teamwork, this operation was carried out safely.”
The Department of Emergency Management advised the public to use caution when reentering homes and neighborhoods; watch for debris, mud and damaged infrastructure; avoid standing water; and report hazards such as downed lines, unstable structures and other unsafe conditions.
The city said it would continue inspections and cleanup to ensure roadways and public areas remain safe.
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