The 2005 Atlantic hurricane season was the most active and destructive on record. One of the factors that likely contributed to this record-breaking season was the presence of exceptionally warm sea surface temperatures (SST) in the tropical North Atlantic. Two long term moored buoys were well positioned to record the anomalous atmospheric and oceanic conditions associated with this warm event. Here we present results from a mixed layer heat budget analysis based on measurements from these buoys. We find that the primary cause of the anomalous warming was a weakening of the northeasterly trade winds and an associated decrease in latent heat loss from the ocean. Important secondary factors include changes in shortwave radiation and horizontal oceanic heat advection.