A Hawaiian Airlines flight encountered severe turbulence after a “cloud shot up vertically” in front of the plane on Dec. 18, resulting in injuries to 25 people, a preliminary National Transportation Safety Board report said.

The independent federal agency released the report Friday on Hawaiian Airlines Flight 35, detailing the weather conditions at the time of the turbulence.

A Hawaiian Airlines Airbus A330 captain told investigators that the plane was traveling at a flight level of about 40,000 feet above a cirrostratus cloud layer. Flight conditions were smooth with clear skies and the weather radar was on when a cloud shot up vertically like a plume of smoke in front of the plane in a matter of seconds, the report said.

There was not enough time to change course, the captain said. He called the lead flight attendant to advise her that the plane might be hit with turbulence. Then, within one to three seconds, the aircraft experienced “severe convectively induced turbulence” at about 10:07 a.m.

The plane — en route to Honolulu from Phoenix — was about 65 nautical miles north-northeast of Kahului at the time and approximately 40 minutes from landing at Daniel K. Inouye International Airport in Honolulu.

Shortly after the sudden turbulence, the lead flight attendant informed the flight crew that there were multiple injuries in the cabin. Of 291 passengers and crew aboard the flight, 25 people sustained injuries. Of those injured, four passengers and two crew members were seriously hurt, and 17 passengers and two crew members suffered minor injuries. The aircraft sustained minor damage.

Investigators conducted a post-accident examination of the weather in the area that revealed an “occluded frontal system with an associated upper-level trough moving towards the Hawaiian Islands. Satellite and weather radar imagery and lightning data depicted strong cells in the vicinity of the flight,” the report said.

Also, at the time of the incident, the U.S. National Weather Service had issued a significant meteorological warning for “embedded thunderstorms with tops reaching FL 380 (flight level at 38,000 feet)” over the region.

The NTSB preliminary report indicated prior to the incident there were no pilot reports of severe turbulence along the route.

An NTSB spokeswoman said an investigation typically takes a year or two to complete, when a final report on the probable cause is expected to be released. A Hawaiian Airlines spokesperson declined to comment on the agency’s preliminary report because of the ongoing investigation.

NTSB Preliminary Report – HA Flight 35 by Honolulu Star-Advertiser on Scribd