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Ironman could get a bit wet

  • LAURA RUMINSKI/West Hawaii Today

    Rain falls as a bicyclist makes his way along Queen Kaahumanu Highway in preparation for Saturday’s Ironman.

KAILUA-KONA — A bout of bad weather could impact West Hawaii on Saturday as some 2,500 athletes take on the 40th annual Ironman World Championship.

“There’s a chance there could be some heavier showers or maybe a thunderstorm popping up for the leeward side,” said Matt Foster, a meteorologist with the National Weather Service in Honolulu.

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The foul weather, based on forecast models available Wednesday, should hold off for a chunk of the athletes to finish, he said. Typically, professionals who get underway at 6:45 a.m. tend to cross the finish line about eight hours later, between 2:30 and 3 p.m.

“Maybe, the first people in, they might be able to avoid it,” Foster said.

The chance for bad weather during the race is possible thanks to a trough of low pressure forecast to develop over the western islands and shift eastward over the state toward the Big Island today through Saturday. At the same time, moisture pooling south of the state is expected to move northward, resulting in stormy conditions for Oahu, Maui County and the Big Island on Friday and Saturday.

“The most unstable conditions appear to be moving through Saturday afternoon across Maui County and the Big Island, where a thunderstorm can’t be ruled out either,” forecasters wrote in an area forecast discussion issued Wednesday.

Saturday morning should open to sunny skies and fairly light and variable winds, with some land breezes coming down the mountain.

A moderate south-southwest swell is forecast to impact the Kailua-Kona coastline as swimmers take to Kailua Bay for the 2.4-mile swim Saturday. Wave heights could be between 5 and 6 feet, according to forecast models. A high tide of 2.14 feet is expected about 5:12 a.m.

“There could be a little bit of waves out there,” Foster said.

A shift in the wind direction is likely by about 10 or 11 a.m. as the triathletes are taking part in either the bike or run, at which point the wind will be coming on land from the ocean, or from the west, Foster said. No wind advisories are anticipated. Winds are expected to be about 8-11 mph in Kailua-Kona that day.

“Wind shouldn’t be much of a factor — even when you get up to Hawi and places that are a little more exposed to the trade winds,” Foster added.

In conjunction with the wind change, cloudiness is forecast to increase. By the afternoon, air heated by the Earth’s surface, on-shore breezes and the instability in the atmosphere could trigger in a storm or two.

“They might pack a little more punch than normal,” Foster said.

Forecast models on Wednesday indicated the afternoon storms could drop 1.7-1.8 inches of rain over leeward areas.

The temperature Saturday is forecast to be about average, or about 80 degrees, with a high of about 86 degrees and low about 74 in Kailua-Kona, according to the National Weather Service.

It’s usually a little cooler to north near Kawaihae, where the temperature averages 76 degrees, and Hawi, where it’s usually about 74.3 degrees, according to the National Climate Data Center.

Typically, precipitation is nil, with areas along the course seeing no more than 0.04 inches that day on average, according to the climate center.

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Ironman World Championship officials said it has a number of contingency options it considers should inclement weather pose a safety concern for athletes.

Email Chelsea Jensen at cjensen@westhawaiitoday.com.