A study of the influence of shear on the Rapid Intensification of Tropical Cyclones using HWRF system

In our recent case study of Hurricane Earl (2010), we proposed a new pathway for asymmetric rapid intensification in sheared storms (Chen and Gopalakrishnan, 2015). This pathway requires cooperative interaction of the convective-scale subsidence, resulting from convective bursts (CBs) and the shear-induced mesoscale subsidence. When CBs are concentrated in the downshear-left and upshear-left quadrants, the subsidence warming is maximized upshear and then advected toward the low-level storm center by the storm-relative flow at the upper level. However, several storms do not rapidly intensify under weak or moderate shear. For instance, Hurricane Isaac (2012) was predicted to be a major hurricane after it emerged into the Gulf of Mexico due to warm SST and reduced shear, yet, it never became a major hurricane in its life cycle. In this study, we will examine the role of shear in intensifying and non intensifying storms using the same framework that we used for understanding the rapid intensification of Earl. There are extensive observations from both the satellites and the air crafts available for Isaac. We will verify the HWRF forecast against observations. Then we will perform similar diagnostics to identify the causes on why Isaac did not go through RI like Earl.