Impact of Enhanced Atmospheric Motion Vectors on Forecasts of Rapid Intensification of Hurricane Gonzalo with HWRF

Impacts of assimilating enhanced satellite-derived atmospheric motion vectors (AMVs) on the numerical prediction of the rapid intensification (RI) of Hurricane Gonzalo (2014) are examined. The enhanced AMVs benefit from special data processing strategies, and are assimilated into the NCEP operational Hurricane Weather Research and Forecasting (HWRF) model using a gridpoint statistical interpolation (GSI)-based ensemble-variational hybrid system. In addition to all other data routinely assimilated into the HWRF, two experiments are performed assimilating different subsets of enhanced AMVs: data from all tropospheric levels (1000-100hPa) and from the upper levels only (350-100hPa), with the recognition that the upper-level data are more numerous in the hurricane inner-core region due to the convective cirrus canopy.

It is found that the assimilation of the enhanced AMVs from all levels improves the track, intensity and structure forecasts during the RI of Hurricane Gonzalo. The assimilation of the AMVs from the upper levels only also results in comparable positive impacts on the intensity and structure forecasts, but its impact on track forecasts is smaller than that with assimilation of the data from all levels. Further diagnoses show that assimilation of enhanced AMVs better represents the vortex secondary circulations and midlevel moisture conditions, leading to stronger convective activity around the storm center and upward energy transport that produces enhanced upper-level warming in the core region. This upper-level warming causes a drop in sea level pressure and thus results in improved RI forecasts.