Ensemble Forecast of Hurricane Edouard (2014)

HWRF ensemble forecasts of Hurricane Isaac (2012) are examined to study why Isaac did not undergo rapid intensification despite favorable environmental factors. Three groups of ensembles are generated: one with HWRF members driven by GEFS ensemble members, another using GEFS ensemble members with boundary layer perturbations, and a third using GEFS ensemble members with SAS (simplified Arakawa-Schubert) cumulus scheme perturbations. The members in each group with the fastest intensification rate are composited as the RI group and the members with the slowest intensification rate are composted as the non-RI group. These groups are compared to determine if there are systematic differences in the radial and azimuthal distribution of deep convection between RI and non-RI members. The comparison of these groups shows that deep convection concentrates downshear for non-RI members and left of shear for RI members. As deep convection moves downstream cyclonically to upshear-left for non-RI members, it tends to propagate outward and resides outside of the RMW. The deep convection in the upshear-left quadrant within the RMW for non-RI members is significantly less than that in RI members. Further diagnostics are needed to address what large scale factors govern the convection pattern, and whether this approach could yield some value for predicting RI.