Storm Mauri in 1982 got strength from the remnants of hurricane Debby

All the model runs in the study were able to forecast the development of Debby and Mauri only two days in advance which indicates poor predictability during the event.

Storm Mauri, which occurred in Northern Finland on 22 September 1982, is one of the most intense windstorms in Finland; it caused millions of cubic metres of forest damage and two fatalities. Mauri is also the only known windstorm in Finland which is speculated to have origins from the remnants of a hurricane. Despite of that, there is no prior research about this event. In a recently published case study, the development of storm Mauri and its predecessor hurricane Debby were investigated.

Debby transformed from a hurricane to an extratropical cyclone (now called ex-Debby) near the US eastern coastline and while weakening, it travelled across the Atlantic to the east. However, over Ireland ex-Debby started to re-intensify rapidly when another large low-pressure system approached from the northwest and strengthened ex-Debby. Ex-Debby then travelled through Sweden to Northern Finland and continued to intensify.

"Even though the other low centre possibly might have caused strong winds in Lapland on its own, the explosively intensifying ex-Debby elevated the winds to a storm which caused extensive damage," says Terhi Laurila, research scientist at the Finnish Meteorological Institute.

The results indicate that storm Mauri was very poorly predictable which was mostly because of the small scale of ex-Debby and the critical moments in its development related to the other low-pressure system. In order to better understand the role Debby played in causing storm Mauri to develop, the events should be investigated with an ensemble sensitivity analysis.

Further information:

Research scientist Terhi Laurila, Finnish Meteorological Institute, terhi.laurila@fmi.fi, tel. +358 50 4648812

Reference: Laurila, T.K., V.A. Sinclair, and H. Gregow, 2020: The Extratropical Transition of Hurricane Debby (1982) and the Subsequent Development of an Intense Windstorm over Finland. Monthly Weather Review, 148, 377-401, https://doi.org/10.1175/MWR-D-19-0035.1