Initial condition sensitivity of the structure of Hurricane Irene (2011)

In August 2011, Hurricane Irene made landfall on the east coast of the United States, first in North Carolina as a category one hurricane, then as a tropical storm near New York City about 24 hours later. In the days leading up to landfall, Irene underwent structural changes, evolving from a smaller hurricane with a tight core of strong hurricane-force winds, to a large hurricane with a broad and diffuse wind field that lacked deep inner-core convection. These structural changes can be difficult to predict, and in Irene's case, the intensity of the storm was largely over-predicted by operational forecasting models with few capturing the large expansion of the wind field. In this study, we explore the environmental influences (such as upstream shortwave troughs) on this structural evolution by perturbing the initial synoptic-scale conditions using the Advanced Research Weather Research and Forecasting model (WRF-ARW). The perturbed simulations from WRF-ARW are compared against an unperturbed control simulation, the National Center for Environmental Prediction's (NCEP) Global Forecast System (GFS) and are verified against best-track data. The impacts of the initial condition perturbations on quantities such as the wind shear magnitude and direction, and the impacts on the evolution of Hurricane Irene will be discussed.