The National Weather Service issued a flash flood warning for Pearl City and other areas of Oahu until 1:15  a.m. as what forecasters describe as "spotty" thundershowers moved on- and off-shore throughout the day.

The warning also  includes Kailua, Honolulu, Mililani and Waipahu as radar showed heavy rain over the areas.

Thunder could be heard and lightning seen off shore of Oah earlier in the evening. During the day, the storm brought on- and off-again rain to parts of Oahu, Moloka and the Big island.

Forecasters say scattered heavy rain showers are expected to continue through the night and the state remains under a flash flood watch through Thursday night.

"The potential for heavy thundershowers and storms exists right on through tomorrow," said Jonathan Hoag, a forecaster with the National Weather Service. "There’s still a concern since the potential is there."

Forecasters say the heavy showers and thunderstorms will be "spotty and localized," with one area flooding while nearby areas remain dry. The unstable weather conditions are created by warm, moist air moving up from the southeast hitting cold air from northwest over the islands.

"They (thunderstorms) can pop up," he said. "You don’t really have much of a pattern when you have unstable conditions … When the atmosphere is unstable, they (thunderstorms) form kind of wherever they will."

A winter storm warning was in effect for Big Island summits, where snow could fall.

Heavy rain fell on the Big Island last night and Windward Oahu and the Koolaus this morning. The weather service issued a flood advisory at about 7 a.m. for Windward Oahu between Punaluu and Kahaluu because of heavy rain, but canceled it as the rains cleared.

More than an inch of rain fell at the St. Stephen’s rain gauge just below the Pali in the 12-hour period ending at 8 a.m. The weather service said showers also fell on the west slopes of the Big Island last night, where 1.8 inches fell at the Pohakuloa Keamuku gauge.

The threat of heavy rains should clear by Friday or Saturday, Hoag said. But the atmosphere will still be moist and winds will likely be from the southeast through Saturday.

Conditions may be humid, with the chance of showers through the weekend.