Analysis of a Panama Bight mesoscale convective system developing into a hurricane-producing east Pacific easterly wave using WRF at convection-resolving scales

Mesoscale convective systems (MCSs) that regularly develop along the coast of South America due to the Andes Mountains have been hypothesized to grow into east Pacific easterly waves (EWs) without the influence of African EWs. This EW genesis pathway is investigated by analyzing the formation of an EW associated with the genesis of Hurricane Carlotta (2012). The Weather Research and Forecasting (WRF) model is employed at high spatial resolution (4 km) to simulate the transition of the MCS into an EW and eventually Carlotta, with ERA5 reanalysis and CMORPH precipitation data serving as the baseline for comparison. A vorticity budget is used to diagnose the growth of the MCS vortex both in reanalysis and in WRF. The disturbance vortex seems to intensify and widen due to mid-level vortex stretching associated with convection, while its propagation is mostly related to horizontal advection, consistent with previous work. Vertical profiles centered on the disturbance suggest that both stratiform and convective structures are present in its development, and that the system tends to become more bottom-heavy over time. An examination of the low-level wind and vorticity structure highlights the potential influence the Papagayo and Chocó jets may have in influencing growing MCSs and EWs. These results support MCS growth as a viable mechanism to east Pacific EW genesis, and a better understanding of the variability of this process may aid in our ability to forecast tropical cyclone activity in the region.