| Summary: | An intense storm named Mauri swept over Lapland, Finland on the 22nd of September 1982 causing 3 Mm3 forest damage and two fatalities. There were thoughts that Mauri originated from a category 4 hurricane Debby but the linkage between Debby and Mauri and their connection to climatic conditions have not been investigated before. In this thesis, a climatic overview of September 1982 in comparison to 1981-2010 Septembers is provided. The calculations are based on ERA-Interim reanalysis data produced by European Centre for Medium-Range Weather Forecasts. The track of the storm is determined from ERA-Interim data from the time Debby occurred until Mauri crossed Finland. The evolution of Debby is also presented with the storm track data by National Oceanic and Atmospheric Administration to comparison. Extratropical transition (ET) and phase diagram of Debby and the synoptic evolution of Mauri are examined. ET is defined to start when the cyclone loses a symmetric hurricane eye feature to form asymmetric fronts, and ET is completed when the warm core of the storm turns cold. A comparison between Mauri and two other intense storms that have affected Europe is briefly presented. It was discovered, that Debby completed ET before rapidly crossing the North Atlantic. However, near the UK ex-Debby started to lose its cold core and asymmetric structure typical to an extratropical cyclone. Ex-Debby phased back to warm cored while crossing Sweden, and at the same time it was rapidly deepening up to 27 hPa in 24 hours defining the storm as a meteorological bomb. Ex-Debby developed a frontal structure along a pre-existing cold front before hitting Lapland. It merged with the pre-existing low pressure center from the Norwegian Sea and proceeded right ahead of an upper trough, a region for cyclogenesis. These made the storm, now named Mauri, more intense as it crossed Lapland, and led to 30 m/s winds based on Finnish Meteorological Institute. Meanwhile, an occluded bent-back front approached Mauri, wrapped around the storm trapping ...
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