Convectively Coupled Kelvin Wave Influence on the Probability of Tropical Cyclogenesis associated with African Easterly Waves

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). This study explores in more detail how the probability of tropical cyclogenesis associated with favorable AEWs (based on invests) is influenced by different phases of CCKWs. The major conclusions are:

• The highest probability of genesis within 2 days is found when invests are approaching convectively active phase of CCKW.
• Probability increases with CCKW amplitude.
• Lowest probability of genesis within 2 days is found when invests are approaching or are in the suppressed phase of CCKW.
• Invests are ~4x more likely to develop within 2 days when they are initially ahead of the active phase of a strong CCKW compared with when they are ahead of or in the suppressed phase.

These results strongly suggest that CCKWs should be monitored in real time in the tropical Atlantic and, together with assessment of the phase relationship with AEWs, probabilistic guidance can be obtained for tropical cyclogenesis.