Causes of the Unusually Destructive 2004 Atlantic Basin Hurricane Season

Abstract

The 2004 Atlantic basin hurricane season was one of the most active on record with nine hurricanes and six major hurricanes (maximum sustained winds > 49 ms1) forming during the season. All six major hurricanes formed during August and September, causing this two-month period to be the most active on record. The primary reason the 2004 hurricane season will be remembered, however, is because of the four hurricanes that devastated the Caribbean and the southeastern United States (Hurricanes Charley, Frances, Ivan, and Jeanne). Estimated total U.S. hurricane damage was between $40 and $50 billion, and much additional damage was sustained in the Caribbean. It is shown that a very strong central Atlantic equatorial trough, associated with anomalously warm tropical Atlantic sea surface temperatures and anomalously weak tropospheric vertical wind shear, combined with extremely favorable midlatitude steering conditions to allow many of the Africa-spawned easterly waves to develop into major hurricanes in the central Atlantic. These major hurricanes then moved on long west-northwest tracks that brought them through the Caribbean and across the southeastern U.S. coastline. The very active and destructive 2004 Atlantic basin hurricane season is attributed to two primary features: a strong Atlantic equatorial trough and steering currents that caused hurricanes to track westward across the U.S. coastline.