A winter storm in the middle- to upper-atmosphere that is bringing rain to the eastern part of the state Tuesday is also causing icing and turbulance for aircraft and may dump up to six inches of snow on the summits of Mauna Loa and Mauna Kea.

The storm is about 15,000 to 20,000 feet above sea level and is moving south after forming in the jetstream to the northeast, forecasters with the National Weather Service said.

The storm will bring cooler temperatures to Oahu, in the 60s, but not as low as Monday night when Honolulu Airport reported a low of 64.

It could also bring heavy showers, thunderstorms and flash flooding to Maui and the Big Island Tuesday night.

Heavy rains were already falling in Hamakua on the Big Islands. The Weather Service issued a flash flood watch for Maui and the Big Island from midnight Tuesday. The flood threat will diminish Wednesday afternoon.

The Weather Service has also issued a winter storm watch for Mauna Kea and Maune Loa summits from midnight Tuesday because of the potential for significant snow, sleet or ice.

The same system will bring more high clouds for Wednesday but could dissipate later in the day.

"There may be a break in the high clouds that are over us in the second part of the day," said Weather Service lead forecaster Tom Birchard

Meanwhile, the public should be prepared for potentially damaging high surf on Oahu’s north and west shores tomorrow that could cause coastal flooding, damage to homes, and road closures Wednesday.

The National Weather Service has issued a high surf warning from noon Wednseday for north- and west-facing shores of Oahu, and parts of Kauai, Molokai and Maui. The warning was set to expire at noon Friday.

Surf will increase rapidly Wednesday evening, reaching 30 to 40 feet along north- and west-facing shores on Kauai, 25 to 35 feet along the north shore of Oahu, and 20 to 30 feet along the west shore of Oahu and north shores of Molokai and Maui.

A storm with hurricane-force winds to the northwest of Kauai generated this swell, which is expected to reach Kauai first and work its way down the island chain. 

The swell has a westerly component that will produce larger than normal surf along west-facing shores and possible wave run-up on Leeward Oahu, the Weather Service said.

"Although previous warnings did not produce many problems for Oahu residents this high surf event has the potential to generate coastal flooding, cause damage to homes located on or near affected beaches, create road closures and other hazards," the city Department of Emergency Management said.

Residents are urged to take measures to protect their property and prepare to evacuate if necessary, the department said. Motorists driving along affected shores should exercise caution as roads can become blocked with sand and debris.