High Resolution Simulation of Rainfall Distribution from Landfalling Tropical Cyclones: Hurricane Irene (2011)

Abstract:

Hurricane Irene (2011) made the first landfall in North Carolina as a category 1 hurricane and continued northeastward along the east coast of the United States. It produced copious rainfall along its track and was responsible for 41 direct deaths and economic losses around 4.3 billion dollars in the US. The Advanced Weather Research and Forecasting (WRF) model was used in this study to investigate the rainfall distribution of Irene. Compared with Stage IV rainfall, the WRF simulation showed the capability of reproduction of the spatial rainfall distribution. It was further proved through the comparison of hourly rainfall from the simulation and rain gauges. The two had a correlation coefficient of 0.62 and a root mean square error (RMSE) around 4.4 mm h^-1. Through a Lagrangian approach in both simulated and Stage IV rainfall, it was found that most of Irene rainfall was concentrated in the front quadrant, especially in the front-left quadrant. The examination of the synotic-scale environment showed that a deep baroclinic zone was developed and strengthened in the front-left quadrant of Irene through the interaction with a mid-latitude trough, creating an environment beneficial for rainfall production in this region. The baroclinic environment promoted the extratropical transition (ET) of Irene, accompanying with more rainfall production in outer front-left rainbands. The rainfall amount in the inner rainband showed a strong correlation with Irene intensity through the lower thermal wind. A non-terrain experiment was set up to study the impact of topography (i.e., northern Appalachians) on rainfall distribution. Compared with the simulation using original terrain, the non-terrain simulation produced a slightly different track and reduced total storm rainfall around 100-200 mm in northern Appalachians.