A slow-moving cold weather system is sweeping across Hawaii, delivering heavy rain, thunderstorms and strong winds statewide through the middle of the week. Forecasters said that significant flooding was possible and that more than half a foot of snow could fall on the Big Island’s highest summits.
The system — known as a kona low — is a major weather maker in the Hawaiian Islands. Tony Fracasso, a meteorologist at the Weather Prediction Center, said these systems are known for producing widespread and sometimes torrential rainfall during the winter months.
“They tend not to move very quickly,” he said.
The system developed over the weekend and by Monday was sitting northwest of Kauai. Forecasters said periods of moderate to locally heavy rain, along with isolated thunderstorms, were expected to continue as the system shifted southward near the western end of the state. A related weather front was also pushing slow-moving showers and thunderstorms across the islands through Monday night.
With rainfall expected to continue through at least Tuesday, forecasters warned that flooding was possible, especially over Kauai County and along southeast and eastern exposures of Big Island and Maui County. Forecasters said roads in flood-prone areas may be closed because of runoff, and overflowing streams and rapid water flow could lead to significant flooding, property damage and landslides, particularly in steep terrain. A flood watch was in effect for all of the Hawaiian Islands through Monday afternoon, and forecasters said it may be extended into Tuesday.
At the same time, winds are forecast to strengthen from east to west across the state, becoming most intense on the Big Island’s summits from Monday night into Tuesday. A high wind warning was in effect through Tuesday morning, with winds between 40 and 60 miles per hour expected, and gusts reaching up to 75 miles per hour.
The strong winds were expected to coincide with hazardous winter weather conditions at higher elevations. Forecasters said periods of heavy snow and ice were expected on the Big Island’s summits, prompting the close of summit roads. Deep moisture being drawn northward ahead of the kona low was forecast to produce up to 10 inches of snow above 11,000 feet on Mauna Loa and Mauna Kea where a winter storm warning was in effect through Tuesday morning.
Significant accumulations of rime ice — an opaque coating of tiny, white, granular ice particles caused by the rapid freezing of supercooled water droplets on impact with an object — were also expected on the summit’s roadways.
Forecasters also said that the combination of heavy snow and strong winds could result in blowing snow and sharply reduce visibility, with brief periods of near zero visibility possible.
Mr. Fracasso said the kona low appeared to have reached its peak on Monday and was expected to gradually weaken in the coming days.
“I don’t think it’ll hang around that much longer, maybe for the next two or three days,” he said. “It’s going to drift to the southwest, and then maybe the south before it dissipates.”
Nazaneen Ghaffar is a Times reporter on the Weather team.
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