On cyclones entering the Baltic Sea region

Trends in the frequencies, durations, mean and minimum sea level pressures, and cyclone formation point sea level pressures of relatively strong (mean sea level pressure < 1000 hPa) cyclones entering the Baltic Sea region between 1948 and 2010 were subject to analysis. Incoming cyclones were divided into ten clusters based on their formation points using the k-means clustering method. Changes in cyclone activity were compared with the North Atlantic Oscillation index. Although the incoming cyclone frequency did not change over the study period, over time the incoming cyclones became significantly stronger as they approached the region. There is no reason at present to assume that more cyclones have begun to form in some clusters. Only weak correlations were found between the number of incoming cyclones and the North Atlantic Oscillation index. Nevertheless, the overall tendency was for fewer but stronger incoming cyclones when the North Atlantic Oscillation index was positive.