Predictability and Dynamics of the Record-Breaking Intensification of Hurricane Patricia (2015)

In this study, we set out to capture and examine the extreme rapid intensification of Hurricane Patricia (2015), a storm that set many records including intensification rate and intensity in terms of maximum observed wind speed, which was poorly forecasted by all operational models (Rogers et al. 2017). Hurricane Patricia occurred during a strong El Niño event in which the Eastern Pacific Ocean was anomalously warm over a relatively deep layer. These warm ocean conditions certainly played an important role in the intensification of Hurricane Patricia and begin to highlight the multi-scale nature of this event. Using the Penn State WRF-EnKF convection-permitting regional hurricane analysis and forecast system assimilating all conventional observations and airborne Doppler radar observations and through parameter sensitivity experiments, we demonstrate greatly improved analysis and intensity forecasts of Patricia with a 1-km horizontal grid spacing along with a newly proposed surface drag parameterization of Chen and Yu (2016) in which C_d decreases for wind speeds greater than hurricane force. The 1-km simulations are critical to resolve the tight eyewall gradients of Patricia, and to well capture the rapid intensification of Hurricane Patricia following the assimilation of Doppler radar observations for the first P-3 aircraft flight. The need for high density and regular inner-core observation is seen and prediction skill is reduced between P-3 flights or without assimilation of inner-core airborne observations. The EnKF Analysis is then validated against independent observations from the ONR-sponsored TCI field campaign, including high density dropsondes within the inner-core of Patricia.

We further examine the practical predictability and dynamics of Patricia through convection-permitting forecasts initialized prior to Patricia’s historic rapid intensification with the EnKF analysis perturbations. Our primary goal is to assess the ability for NWP models to skillfully forecast this remarkable and anomalous event. In addition, we seek to determine the inner-core dynamics versus environmental conditions necessary for both the rapid intensification and the record observed peak intensity. Our focus is on factors influencing the timing of rapid intensification, the peak intensity, and the intensification rate across the ensemble.