Meteorologist links Siglufjörður storm damage to rotating wind vortices

Meteorologist Trausti Jónsson believes rotating wind vortices caused severe damage in Siglufjörður during Wednesday’s storm, mbl.is reports. The vortices can generate powerful gusts capable of tearing roofs from buildings.

Jónsson said the phenomenon is not unusual in Siglufjörður under certain conditions. It often occurs in east-northeasterly winds, when a strong wind stream runs outside the fjord and along the outer part of the Tröllaskagi peninsula. Swirls can break away from the main stream and rotate around the mountains.

Similar conditions can form where wind blows along a mountain and then reaches a corner, he said, comparing the pattern to Kjalarnes and Hafnarfjall. At those locations it can occur with winds from several directions, while in Siglufjörður the wind must come from the right direction and the air must have the right stability. Whether a vortex passes over a weather station is largely a matter of chance.

Jónsson said Siglufjörður often suffers the greatest damage because the wind direction is particularly unfavourable there, and the town’s terrain and dense settlement contribute to the impact. He also cited similar vulnerable spots in eastern Skagafjörður and around Grenivík, in the outer part of Eyjafjörður.

He has documented around 15 to 20 cases of roofs being torn from buildings in Siglufjörður under similar conditions over the past 100 years. Among the older examples, a 1919 storm caused damage when a shed was blown from its foundations and damaged other buildings. In 1921, a pier broke and a newly built chimney near the church was blown down. A 1922 easterly storm blew away a storage building and damaged others, while roofing materials and sheds were torn away. In 1926, boats and piers were damaged, two buildings under construction were blown down and utility poles broke. A 1929 storm also tore off roofs, damaged boats and buildings, and damaged the state herring-processing plant.