Variability of Atlantic Tropical Cyclone activity in 2012 and 2013

This presentation will focus on the nature and causes of intraseasonal variability of tropical cyclone variability in the past two seasons. Part of the motivation for this work is to better understand the different roles played by the environment versus the weather systems themselves during the HS3 field campaigns in these years. The first part of the work emphasizes the environmental impacts and in particular that associated with the MJO and convectively coupled equatorial waves. For example, an MJO event had a marked negative impact in the 2012 season, suppressing the tropical cyclone activity during the September field campaign. In 2013 it is now well known that the season was much less active than expected given considerations of normal environmental predictors. Several players appear to have impacted this season that includes the MJO, convectively coupled Kelvin waves, and midlatitude troughs. This talk will provide an assessment of these different sources. The second part of the talk will give greater emphasis to the variability of the African easterly waves and their interactions with the environment to understand better the role of the environment at a weather system scale. Here emphasis will be given to the nature of the non-developing AEWS and in particular their interactions with dry air.