By JOHN BURNETT Hawaii Tribune-Herald
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A powerful kona low-pressure storm front is moving down the island chain from the west to the east with strong winds, heavy rainfall and flooding expected.

“For the Big Island, we do have the flash flood watch in effect, primarily for Thursday onward,” Maureen Ballard, forecaster for the National Weather Service in Honolulu told the Tribune-Herald Tuesday. “We’re going to have some breezy, strong winds with that, so that’s going to impact some of the areas that would have some more of the enhanced showers that would form as the winds kind of push things off to the south shore and hit the mountains that way.

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“So we’re talking about multiple floodings that’s going to come in, pretty much in multiple directions — stuff that’s going to be forming overhead plus the influence of the mountains on the island.”

Kawa Flats, between the 58- and 59-mile markers, floods during heavy rain due to poor drainage.

This would be the second kona low to hit the islands this year. A system moving west to east struck the Big Island the first weekend of the year, with Glenwood, in the midst of the upper Puna rainforest receiving 14.21 inches of rain in a 48-hour period ending at 8 a.m. Jan. 6.

During the same period, Laupahoehoe received 10.09 inches, Mountain View reported 8.88 inches, Hilo International Airport recorded 6.67 inches, and Pahala, in the heart of Ka‘u coffee country, measured 6.18 inches.

The major concern, as Ballard pointed out, is flash flooding, which could occur anywhere on the island.

“There are going to be some areas that are a little bit more susceptible to things. For example, with the southeast flow, Kawa Flats on the southeast side of the island is definitely an area that we will be keeping our eye on,” Ballard said. “However, once this rainfall comes in, it could be causing trouble anywhere on the island, especially with some of those thunderstorms that could develop. A thunderstorm could cause additional rain in any area it pops over.

“It’s hard for us to tell exactly where a thunderstorm might develop, and if you are in a thunderstorm, that’s going to have the possibility of producing a lot of rain in a very short amount of time. The greatest threat for that will be Friday and Saturday for the Big Island, but it’s also a possibility for (tonight into) Thursday.”

The seven-day forecast for both Hilo and Kona include the possibility heavy showers starting Thursday and continuing through the weekend.

According to a special weather statement issued by NWS, “Damaging winds will likely be the primary hazard with these storms, though large hail cannot be ruled out.”

It’s been years since the Big Island has experienced hail, although hailstones — rain that has frozen into ice before falling — have fallen in the Saddle area during a thunderstorm.

“What we’re seeing is the potential for these thunderstorms to be strong enough for that. It’s not a huge threat but it’s a possible threat,” Ballard said.

The forecast calls for wind gusts in Kona as high as 44 mph on Friday night and 47 mph on Saturday. Hilo gusts are forecast to be as high as 32 mph on Friday night and 28 mph on Saturday.

In addition, the summit areas of Maunakea and Mauna Loa could see snowfall during thunderstorms and other rainy periods, especially at night.

Email John Burnett at jburnett@hawaiitribune-herald.com.