Interactions between African Easterly Waves and Convectively Coupled Kelvin Waves and the Impact on the Probability of Tropical Cyclogenesis: A Case Study of Cristobal (2014)

Convectively coupled Kelvin waves (CCKWs) propagate in the tropical Atlantic region during boreal summer where they are known to interact with and influence African easterly waves (AEWs). Several recent studies have also highlighted that the probability of tropical cyclogenesis from an AEW is enhanced 2-3 days after the passage of the convectively active phase of a CCKW (e.g. Ventrice and Thorncroft 2012; Schreck, 2015). Recent work by Thorncroft and Brammer (2016) has shown that the outcome (genesis or not) associated with an AEW-CCKW interaction is strongly dependent on the amplitude of each wave. We will further explore the nature of such CCKW-AEW interactions through considering a case study whereby a favorable AEW (for genesis) interacted with the convectively active phase of a CCKW resulting in the genesis of Cristobal in 2014. A detailed analysis of the CCKW and AEW structures will be provided together with an analysis of the interactions. Emphasis will be given to the impact of the CCKW environment on the AEW-associated genesis including consideration of convection and the generation of low-level vorticity, as well as recirculation characteristics following Dunkerton et al (2009).