Dec. 19—The unusually stormy weather that hit a Hawaii-bound flight on Sunday and left dozens of passengers injured came amid forecasters' warnings of a strong cold front leading to downpours, thunderstorms, lightning and severe turbulence. The number and degree of passenger injuries raised questions about how such a dramatic incident occurred.
The National Weather Service had issued a weather advisory for thunderstorms northeast of Maui — which would have included the area in the flight path of the plane coming in from Phoenix at the time it was buffeted by strong winds.
"We don't really get strong thunderstorms that often in Hawaii," said Thomas Vaughan, a National Weather Service meteorologist in Honolulu, said Sunday evening. "We do get them occasionally... it doesn't happen too often here."
Hawaiian Airlines officials called the incident, which is being investigated by the Federal Aviation Administration, an isolated and unusual event.
The plane encountered the turbulence around 10:16 a.m. Hawaii time, Vaughan said, or about half an hour before it landed at 10:50 a.m. The stormy weather by then had prompted the weather service issue several "significant meteorological information" notices, Vaughan said, with the first coming just before 4 a.m. Hawaii time.
Thunderstorms create intense winds at their center that can rise well above 100 miles per hour, said Keith Cianfrani, an aviation safety expert.
"That's enough to snap an aircraft in half," he said. "It's very serious, for any kind of aircraft."
"If you're not seated at time (serious turbulence) happens, you're going to be flying all over the place," he added. "It's not the first time this has happened. You can get injured very seriously."
Hawaiian Air executive vice president and chief operating officer Jon Snook told reporters there was no warning that that "particular patch of air... was in any way dangerous" to Flight HA35, the Airbus A330 aircraft carrying 288 people on Sunday.
Thirty-six people were injured on the Sunday flight as it neared Honolulu, 11 seriously, with 20 taken to the hospital for treatment, officials said. Victims included a 14-month-old child, and injuries included serious head trauma, lacerations, bruising and loss of consciousness, according to Honolulu Emergency Medical Services.
Photos from passengers posted on social media sites appeared to show some damage to the interior of the plane. Airline officials said the seatbelt sign was on at the time the incident occurred.
Turbulence injures roughly 60 people in the U.S. every year, according to the Federal Aviation Administration. The federal agency reported that from 1980 through 2008, U.S. air carriers experienced 234 turbulence accidents, resulting in 298 serious injuries and three deaths.
Richard DiMaio, professor of aviation meteorology at Lewis University and former United flight operations aviation meteorologist, said one key question would be the plane's altitude when it encountered the turbulence.
"If a plane is traveling at cruise altitude, 34,000 to 39,000 feet, it is sometimes easier to circumnavigate a thunderstorm if it is moving slowly," he said. "Since airlines have to follow a certain flightpath below 20,000 feet, there is less room to navigate since they are on a certain "highway" in the sky or an approach fix point," such as coming into an airport, he added.
Conditions such as these happen frequently in the US, but not too often in Hawaii, he said.
"This type of weather system is called a 'Kona Low,'" a cold season event that occurs three or four times a year, he said. "They are called Kona Lows since it produces strong southwest wind from the Kona Side of the Big Island, frequent low-level turbulence and occasional heavy rain."
Hawaiian Airlines tweeted that, "Medical care was provided to several guests & crew members at the airport for minor injuries while some were swiftly transported to local hospitals for further care."
The stormy weather and cold front was expected to bring "numerous showers and thunderstorms" to the region through Monday, the National Weather Service said, with potentially severe stroms Sunday night and Tuesday. Forecasters also warned of possible strong winds and hail and in some cases, with potential flash flooding.
The Associated Press contributed to this story.
St. John Barned-Smith is a San Francisco Chronicle staff writer. Email: [email protected]
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