Birchard said the chance of rain was pretty good.

"But on which island it will fall, and when within that time frame, is impossible to pin down at this point," he said.

He was certain about where the snow, if it comes, is likely to fall: the summits of Mauna Kea and Mauna Loa.

There is a good chance the rain will come down hard, the Weather Service is forecasting.

"We've issued a 'flood potential' outlook," Birchard said. "Flooding rains are possible this week."

Birchard said skies are likely to be clear this morning, with clouds and showers building inland in the afternoon and the weather becoming less stable as the week progresses.

Meanwhile, the surf was high and climbing yesterday on the North Shore. The National Weather Service was forecasting a peak last night or this morning at 15 to 18 feet, measuring from the trough to the crest of the wave on the face.

A high-surf advisory has been issued for the north and west shores of all islands. The surf will slowly diminish through Tuesday, Birchard said.

Shortly after 5 p.m. yesterday, Lifeguard Capt. Bodo VanDerleeden said sets 8 to 12 feet high by local surfers' measure were coming in every 10 to 15 minutes on the north shore of O'ahu, with 6- to 8-foot waves between sets.

"It's a mixed day," he said, "and that makes it kind of dangerous."

Lifeguards were kept busy running interventions, he said, but no one was seriously injured.

VanDerleeden's wave measures were in local surfer style. Generally speaking, the weather service measure is about 1› times the local measure for big waves and twice the local measure for smaller waves.

The National Weather Service said waves hitting the North Shore yesterday at 5 p.m. were 9 to 12 feet high, with occasional sets of 12- to 18-foot waves.