HONOLULU — Severe turbulence on a Hawaiian Airlines flight from Phoenix to Honolulu last month was related to a cloud that shot up vertically, like a smoke plume, according to a preliminary report from the National Transportation Safety Board. 

The report said the Dec. 18 flight, carrying 291 passengers and crew members, was about 40 minutes from landing at the Honolulu airport when “severe turbulence” injured 25 people, with six serious injuries. 

Parts of the interior of the airplane were damaged. 

The National Transportation Safety Board released its preliminary report on Friday. The final report will take 1 to 2 years to complete and will include probable cause. 

Before the incident happened, the captain said flight conditions were smooth for travel, according to the report.

However, the weather took a turn for the worse. The report said there was not enough time to deviate when a cloud shot up vertically, like a smoke plume, in front of the plane.

After the severe turbulence, the lead flight attendant informed the flight crew that there were multiple injuries in the cabin. 

A post-analysis of radar data from the incident shows the plane was flying through a line of storms from an occluded front.

An occluded front occurs when a warm air mass gets caught between two cold air masses. These fronts are usually responsible for causing strong winds and heavy rain with a thunderstorm possible.

The National Weather Service had issued a warning for embedded thunderstorms.

Radar imagery from the flight showed thunderstorms and lightning. This triggered the National Weather Service to issue a warning for embedded thunderstorms.

Michelle Broder Van Dyke covers the Hawaiian Islands for Spectrum News Hawaii. Email her at michelle.brodervandyke@charter.com.

Spectrum News Senior Producer and Meteorologist Keith Bryant contributed to this story.