A leading contributor to the increased activenes of the North Atlantic basin seasonal tropical cyclone actvity ove rthe past 20 years has been the warming of the North Atlantic basin caused by the warm phase of the Atlantic multi-decadal oscillation.

After a brief period of moderately intense warm phase of the Pacific decadal oscillation neutral phase has returned. During the past 2 decades the character of PDO has changed...weaker and shorter duration events where as previous patterns had a tendency to lock into warm or cool phase with intensity.