HILO >> The hurricane warning for Hawaii island was downgraded to a tropical storm warning late Thursday afternoon, but the torrential rain that soaked the windward side this week are expected to continue and might even drench portions of the island through the weekend.

Mayor Harry Kim said the slow progress of Hurricane Lane off the western coast was developing into the “worst case” scenario for the island Thursday because the pause allows it to dump enormous amounts of rain on the eastern side of the Big Island.

Kim said Thursday he was less worried about wind damage and more concerned about flooding after more than 20 inches of rain fell on some windward communities. Lane was moving at only 6 mph, and “it’s almost like stationary,” he said.

“I told our group this morning, this is the best scenario for west side and Oahu and the rest but the worst-case scenario for us,” Kim said. “This is going to hang. The only thing I can’t tell you is how long.”

The east side of the island from Hamakua to Volcano remained under a flash flood warning Thursday night as pounding rain generated runoff that roared down drainage channels and streambeds, and completely overwhelmed some drainage systems. Civil defense officials warned the public to stay off the roads unless absolutely necessary.

County officials opened a shelter at Waiakea High School to respond to the threat from flooding, and nine people had checked into the facility by Thursday afternoon. Five other shelters had already opened in West Hawaii, county officials said.

Among the hard-hit areas was the upscale Reed’s Island neighborhood in Hilo, where county firefighters responded Thursday afternoon to a request for help from a family of five that was trapped in a home by rising floodwater, said Fire Battalion Chief Matthias Kusch.

Kusch described the incident as “an assist, because their road has become a stream.” The family was staying at a home on Kaiulani Street, he said.

Waiakea Uka resident Shannon Matson put out an urgent call Thursday for sandbags to try to protect the Reed’s Island home of a longtime friend but said civil defense and fire officials told her they couldn’t help. She posted video of water rushing down the street and undercutting the foundation of another home nearby, and “the driveway is completely washed away and the foundation is completely compromised,” she said. Her friend’s home is on Kaiulani Street downslope from the first home, and floodwater was flowing from the front of the upper home into the lower one.

“The house is pretty bad right now,” Matson said in an interview. “My husband is there currently. We’re trying to mop out and soak out some of the water, and trying to find some sandbags or something to block more water from coming in. … We’re just trying everything we can to help.”

Matson said she was told the problem was caused by a clogged drainage system up the road, and she was unable to find sandbags anywhere in Hilo to block the flood of water.

Kim told his staff at Hawaii County Civil Defense that “things like Reed’s Island may happen again because of a simple plug or whatever.”

A Fire Department helicopter also rescued a pair of hikers who spent the night on a ridge above Waimanu Valley. The hikers were trapped in the area after rainfall caused a stream to swell and blocked their exit, and they were extracted at about 12:30 p.m. Thursday, Kim said. Two other hikers were also trapped in the same area but took shelter in a home nearby, he said.

Torrential rain in East Hawaii Wednesday night and Thursday caused landslides and flooding that closed an array of roads in Puna and Hilo. In the 24 hours ending 8:45 a.m. Thursday, Lane dumped 18.82 inches at a monitoring station in Waiakea and 14.69 inches at Hilo airport, and extremely heavy rain continued throughout Thursday.

The National Weather Service predicted Lane would dump an additional 12 to 18 inches of rain on northern and eastern Hawaii island in the 24 hours ending this morning.

A landslide triggered by heavy rainfall severed Highway 19 near mile marker 13 at 3:45 a.m., temporarily cutting off the primary access route between Hilo and Waimea, and another landslide later in the day closed Akoni Pule Highway at the 24-mile marker in North Kohala.

Other early morning road closures caused by flooding included Laupahoehoe, Akolea and North Kulani roads as well as East Kawailani Street and Bayfront Highway in Hilo, which regularly flood during heavy rain. Kim said many smaller roads within Puna and Hilo subdivisions have become impassable because of the heavy overnight rain.

“I don’t know what nature has in mind,” said Kim. “All I know is this is a huge system and it’s stalled right there.”