The slow progress of Hurricane Lane off the western coast of Hawaii island is developing into the “worst case” scenario for the island because the pause in the progress of the hurricane is allowing it to dump enormous amounts of rain on the East side of the island, said Mayor Harry Kim today.

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

“That’s a very rare thing for a hurricane this size,” Kim said. “I’ve never seen that around here.”

“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 North Kohala to Kau is under a flash flood warning as pounding rain generated runoff that is roaring down drainage channels and stream beds, and completely ovewhelmed some drainage systems.

County officials opened a shelter at Waiakea High School this afternoon to respond to the threat from flooding. Five other shelters have already opened in West Hawaii, but only 22 people were staying there as of 2 p.m. today, county officials said.

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

He 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.

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, at about 12:30 p.m. he said. Two other hikers were also trapped in the same area, but took shelter in a home nearby, he said.

“Things like Reed’s Island may happen again because of a simple plug (in the drainage system) or whatever,” Kim said.

Torrential overnight rains in East Hawaii caused a landslide and flooding that closed an array of roads in Puna and Hilo, but that mess will probably be dwarfed by what lies ahead today and tonight as powerful Hurricane Lane creeps closer to the islands.

The National Weather Service predicted Lane will dump an additional 12 to 18 inches of rain on north and east Hawaii island in the next 24 hours, prompting some gasps from the audience at a morning briefing today at Hawaii County Civil Defense headquarters.

The hurricane system will deposit another 18 to 24 inches of rain on the southeast portion of the Hawaii island over the next 24 hours, and dump another 8 to 10 inches on West Hawaii, said Deanna Marks, official-in-charge of the Hilo Data Collection Office for National Weather Service.

Lane has already poured more than a foot of rain on portions of the island during the past 24 hours, including 12.43 inches in Waiakea Uka above Hilo, 13.28 inches at Hilo airport, and 17.68 inches at the Waiakea Experimental station gauge.

Flash flood warnings are already in effect from Hamakua to Volcano.

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

A landslide triggered by heavy rainfall severed Highway 19 near mile marker 13 at 3:45 a.m., cutting off the primary access route between Hilo and Waimea. Other early morning road closures caused by flooding included Laupahoehoe Road, Akolea Road and North Kulani Road, according to civil defense officials.

Other closures included East Kawailani Street and Bayfront Highway in Hilo, which regularly flood during heavy rains, but Kim said many smaller roads within Puna and Hilo subdivisions have become impassable because of the heavy overnight rains.

“We have numerous closures,” Kim told about 75 people gathered for the morning briefing. He said flooded small roads were reported in the Hawaiian Beaches, Fern Acres, Orchidland, Paradise Park and others.

Hawaii island Police Chief Paul Ferreira said police were notified of four people who were trapped in Waimanu and Waipio valleys on the northeast side of the island last night. A fire department helicopter was dispatched this morning to search for the two pairs of hikers, according to a fire spokesman.

“This is a huge, huge system that is there, and it is stalled at 7 mph,” Kim said. “Lord knows how long it will stall.”

National Weather Service is predicting the onset of damaging tropical storm force winds for the island from 2 p.m. to 8 p.m., starting at the southern part of the island and moving up the west coast. There is a potential for gusts of up to 65 mph for the west side of the island — Marks called that a “worst-case scenario” — and up to 50 mph for other parts of the island.

Rain bands will continue to move across the island today, and the flash flood warning for the island that is in effect until 9:45 a.m. today likely will be extended, Marks said.

Kim said the slow-moving storm is alarming because “if this stall continues, this rain could stay here for days or weeks.”

“The 7 mph, I’m telling you, is a real first time for me, a major hurricane at this point of the hurricane that slows,” he said. Hurricane Iniki sped up at this point as it moved north along the island chain, Kim said.

”What will happen tomorrow, I don’t know,” Kim said. “The best thing for everybody is rapid movement, and rapid diminishing of the intensity.”