The large hail that pelted Windward Oahu Friday morning enthralled residents and has National Weather Service staffers checking the record books.
"The hail that fell in Kaneohe as far as I know was unprecedented," said Tom Birchard, lead forecaster. "We have never had hail of that size at sea level.
"We think we have a new state record as far as hail size at sea level."
He said that hail storms occur here on the slopes of the Hawaii island volcanoes, but the hailstones usually melt before reaching sea level.
So much hail fell between 6 to 7:30 a.m. Friday that "at some points it just covered the ground," he said.
The weather service has photographs of hailstones that are at least 2 1/2 inches. There is another photograph of a hailstone that is larger, but weather experts aren’t sure if it is two pieces that froze together, he said.
Birchard explained that during a thunderstorm there are strong updrafts of warm air and downdrafts of cold air. Water droplets picked up by the updrafts freeze when carried above the freezing level of 32 degrees fahrenheit.
As the frozen waterdrops fall they may thaw as they move into warmer air. However, the half-frozen water droplets may get picked up in another updraft and carried back up to the cold air refreezing. With each trip above and below the freezing level the frozen droplet gets bigger until it finally falls as hail.
The weather service received reports this morning that a hail storm lasted about 30 minutes.
On Tuesday hail stones — some as large as 1 1/2 inches — fell in Waimanalo, setting a record only to be apparently broken three days later.
Friday’s hail occurred because there were very cold temperatures in the middle and upper portions of the atmosphere, Birchard said, which destabilized the atmosphere, creating very strong updrafts. "That caused hailstones formed in the thunderstorms to recirculate through the thunderstorm and that’s the way they grow," he added.