Composite Ensemble Sensitivity of Atlantic Hurricane Intensification

Prediction of tropical cyclones' (TCs) intensity is a major forecasting challenge. Substantial improvements in the prediction and representation of the large-scale ambient environment have not led to reduced intensity forecast errors in the same steady manner as they have for TC track forecast errors, which suggests that the storm structure plays an important role in the intensity evolution of TCs. Rapid intensification (RI) is particularly difficult to forecast and statistical-dynamical models, such as those of DeMaria and Kaplan, as well as high-resolution numerical modeling studies and satellite observations point to the importance of TC structure in predicting RI.

We have simulated the rapid intensification of seven TCs from the 2009, 2010 and 2011 Atlantic basin hurricane seasons using a 12 km 96-member WRF model ensemble. The statistics of the ensemble are used to investigate the sensitivity of rapid intensification to TC structure and the validity of the results are tested using perturbed initial condition experiments. Composited sensitivity results of six test cases indicate a sensitivity to kinematic and thermodynamic variables in the inner core as well as to moisture in the rainband region at two to three times the radius of maximum wind. Perturbed initial condition experiments in which perturbations in moisture are withheld show that the dry dynamics play a relatively greater role in the intensifying hurricanes. An equivalent potential temperature budget of a high-resolution (4/3 km) ensemble is investigated to more completely understand the mechanisms at work.