The state is under a flash-flood watch through Thursday after heavy rain hit parts of Windward O'ahu and Kaua'i yesterday.

Garden Island officials were preparing to close Kuhio Highway between Hanalei and Princeville late last night after a gauge on the Hanalei River showed water levels near the flood mark, the National Weather Service said.

On O'ahu, the Wilson Tunnel area got 4.33 inches of rain from 2 to 8 p.m., and at one point forecasters estimated rainfall at a rate of 3.76 inches an hour there.

The Luluku area got 3.57 inches of rain during the same period.

The weather service issued a flash-flood warning for Windward O'ahu from Waimanalo to Kahuku. The warning was lifted at 7:45 p.m. However, the weather system moved to Kaua'i and prompted a flash-flood warning there.

More rain is expected this week from a low-pressure system approaching the state from the west, forecasters said.

Roy Matsuda, lead forecaster for the National Weather Service, said a combination of wind direction, low pressure and instability in the atmosphere caused the heavy downpour over O'ahu.

The winds were blowing parallel to the mountains in a southeasterly direction, creating conditions conducive to heavy rains, he said.

"It will make the clouds bigger and the rainfall rate heavier," Matsuda said. "The heaviest will be on the mountain."

The winds may change today, and that would bring better weather, he said. But that may be followed by more rain later in the week.