Caribbean Waves as precursor systems of late season hurricane formation

African easterly waves (AEWs) are prominent features of the summer climate in the African and Atlantic tropical regions. They frequently serve as seeds for tropical cyclones over the Atlantic. AEWs are also important synoptic features in the Caribbean where they can impact rainfall and tropical cyclogenesis. While the nature and variability of AEWs in the African and Atlantic regions are quite well known the same is not true for the Caribbean region. In this study we will combine a climatological analysis of these Caribbean EWs together with a case study approach highlighting the waves in summer 2013.

Regression analysis has been used to highlight the typical evolution of EWs in the Caribbean region and how this varies by month. Indeed, our results show that for the early season, EWs show a coherent development downstream from Africa presenting a classical Riehl structure (Riehl 1954), however, this can't be said for the late season when EWs seem to be generated in situ.

In the second part of this study we will explore the nature of three tropical cyclones that occurred in 2013 to provide a more in depth look at the evolution of the EWs that lead to the genesis of Fernand, Ingrid and Manuel. We will highlight the fact that tropical storm Fernand originated from an AEW but hurricane Ingrid was generated in situ. The genesis Ingrid is quite important since the precursor system also induced the genesis of Hurricane Manuel which caused a total damage of US$4.2 billion dollars in Mexico. Spectral analysis shows that MRG waves were involved in the genesis of this “Caribbean Wave” as Frank had called it (Frank 1972).