Evaluation of Ensemble Forecasts for Tropical Cyclogenesis from African Easterly Waves

Ensemble forecasts of African easterly waves (AEWs) have been analysed across the NCEP Global Ensemble Forecasting System (GEFS) reforecast version 2 for 2002-2015. Vortex based bias statistics have been calculated with respect to tracked AEW vortex characteristics. This vortex based bias analysis highlights issues with AEW forecasts over the Guinea Highlands and the implication of this on downstream TC genesis over the Atlantic. Forecasts for hours 24 - 96 hrs show a strong positive vorticity bias for AEWs as they propagate over the Guinea Highlands. This error then propagates downstream, though doesn't appear to continue to grow over the Atlantic region.

This research focuses on the predictability of the structure and evolution of AEWs as they leave the West African coast. Case study analysis of a non-developing and subsequent developing AEW during 2014 will be presented to highlight differences between systems. These cases will also be used to present new bias corrected ensemble based genesis products.