Atmospheric conditions came together in late July providing a favorable climate for six tropical cyclones — one of which threatened the Hawaiian Islands — to cross the Central Pacific Ocean Basin.
The 2013 Central Pacific hurricane season officially ended Saturday. The six cyclones that either formed in, or passed through, the basin, which extends from 140 degrees west longitude to the International Date Line, exceeded the National Oceanic and Atmospheric Administration’s Central Pacific Hurricane Center’s 2013 hurricane season outlook of one to three tropical cyclones. The basin sees on average four to five cyclones each year.
The 2013 hurricane season’s six cyclones made it the sixth busiest since 1970 — tied with 1971 and 1983, according to the center. It was also the second busiest year since 1998. The most storms in a single season — 11 — occurred in 1992 and 1993.
Mike Cantin, a warning coordination meteorologist with the Honolulu-based hurricane center, said this year’s hurricane season, June 1 to Nov. 30, featured two distinct periods of activity: a very busy stretch of activity that began in late July and lingered through late August and a prolonged quiet period that settled in for the remainder of the season.
“What kicked off this year was a period where the atmosphere just came together — the situation was primed for development,” Cantin told West Hawaii Today on Tuesday. “For two to three weeks, the atmosphere was kind of locked in and things just kind of started spinning up.”
Neutral El Nino Southern Oscillation conditions lingered throughout the season, Cantin said. El Nino, which he said never made an appearance in 2013, often correlates with warmer ocean temperatures that cause increased storm activity.
Despite the neutral conditions this year, as well as slightly cooler waters, favorable climactic conditions during late July through late August helped foster cyclonic activity, he said.
Named storms that either formed or passed through the Central Pacific Ocean Basin in 2013 were Tropical Storm Flossie, which had a life cycle between July 27 and 30; Tropical Storm Gil, which had a life cycle between Aug. 5 and 6; Hurricane Henriette, which had a life cycle spanning Aug. 8 to 11; Tropical Storm Pewa, which had a life cycle between Aug. 16 and 17; Tropical Storm Unala, which had a one day life cycle Aug. 18; and Tropical Depression 3-C, which had a life cycle between Aug. 19 and 20.
Tropical Storm Flossie was the lone cyclone to affect the Hawaiian Islands, Cantin said. He explained that while the storm appeared to be weakening as it moved over cooler waters to the east of the Big Island, favorable upper level atmospheric conditions helped ventilate the storm, providing it with strength as it moved closer. As it neared the island, however, a wind sheer seemed to cut it in half.
There were reports of limited damage on the Big Island including downed trees and power lines, he said. As the storm moved northwest, it passed Maui packing powerful thunderstorms and on Molokai, lightning reportedly struck a power plant, knocking out electricity to the island for a couple of hours.
Three of the storms actually formed in the Central Pacific Ocean Basin this year: Pewa, Unala and 3-C, Cantin said. None affected the islands because they all formed west of the state, near the boundary of the Central Pacific Ocean Basin, he said.
“After late August,” Cantin said, “(the favorable conditions) pretty much shut off.”
While the season may officially be over, Cantin said storms can occur at any time of year, though cold fronts and cooler waters around the state make it difficult for storms to develop that could impact the islands.
“The odds would say and the past history would say that this time of year the chance of one forming near the state and posing a threat is quite low — not impossible — but quite low,” Cantin said.
Forecasters in May predicted a below-normal hurricane season for the basin; calling for one to three tropical cyclones to either form in or pass through the basin. In 2012, forecasters called for two to four storms, but just one, Tropical Storm Daniel formed in July and passed south of the islands.
Cantin said many variables make it difficult for the forecast to be spot on.
“We’re looking at a big season, we weigh the factors, the past history and make the best forecast that we can,” he explained.
Nevertheless, people should always be prepared for fewer or more storms at any given time, Cantin added.
“Even if we forecast a below normal or an above normal season, all it takes is that one storm to clobber us,” he told West Hawaii Today. “Hawaii has a significant history of being impacted by tropical cyclones, namely hurricanes, and it’s going to happen again.”