Cross Season Memory of Ocean-Atmosphere System

For North Atlantic, a structure index related to hurricane activity has been identified. This index represents the final integrated states of ocean-atmosphere system of the last hurricane season, but it plays as a good predictor of hurricane activities of the coming season. Historical data shows that this single index has a better forecast skill than the methods applied by Colorado State University (CSU) to make their June forecast in 1984-2001. More importantly, the forecast based on this structure index is available right after the last hurricane season, which is six months earlier than CSU June forecast. This result indicates that the hurricane related memory of ocean-atmosphere system can last for more than six months and can cross seasons.