The effect of a river delta and coastal roughness variation on a landfalling tropical cyclone

Numerical simulations on an f plane are performed using the Weather Research Forecasting (WRF) model to study how the presence of a river delta and variations in coastal roughness might affect the motion and the structure of a tropical cyclone (TC) near landfall. In each delta experiment, an idealized triangular-shaped delta, pointing to the west with length 150 km and a river mouth size of 100 km, is inserted along the coastline. The surface roughness and the moisture availability of the delta vary among the delta experiments, and the surface properties are uniform in the rest of the land area. In another set of experiments, where there is no delta, the roughness of a whole land area has different values along the north-south oriented coast. Results suggest that the TC in the control experiment (CTRL, with no delta or roughness variation along the coast) is weaker than all the delta cases during a certain period before landfall. Moisture supply from the delta appears to have an effect on sustaining the approaching TC, despite the relatively small scale of the delta. Tracks of the TCs in the roughness variation experiments deviate from that of the CTRL. The roughness variation along the coast apparently affects the convergence patternshigher roughness induces stronger convergence and hence increases the vertical advection term in the potential vorticity tendency distribution over the rougher area. Hence, a TC tends to move toward a region with higher roughness. Copyright 2010 by the American Geophysical Union.