Adjoint Sensitivity Diagnosis of the Intensification of Hurricane Harvey

Hurricane Harvey was a record setting tropical cyclone that underwent rapid intensification prior to landfall in Texas. While numerical weather prediction models anticipated some intensification prior to landfall, the intensity and the rate of intensification were underestimated by most models. This presentation will present the results of adjoint-derived forecast sensitivity diagnosis of the sensitivity of intensity and intensification rate to the initial conditions of simulations of the hurricane for 24 to 36h before landfall. The response functions chosen for this study include the perturbation dry air mass in a column above the tropical cyclone center, the vorticity averaged around the TC center, and the pressure tendency following the cyclone center. Regions of high amplitude sensitivity indicate where small initial condition uncertainties or errors could impact the intensity or intensification rate. Optimal perturbations are derived from the forecast sensitivities to intentionally influence the intensification rate of the simulated hurricane. Diagnosis of the perturbation evolution points to key dynamical processes influencing TC intensification (rate). The implications of the results of these adjoint studies on the efficacy of targeted observing for this cyclone will be discussed.