Track and Structural Changes Associated with Tropical Cyclone Making Landfall Near a River Delta

Numerical simulations on an f plane are performed using the Weather Research Forecasting (WRF) model to study how the presence of a river delta might affect the motion and the decay rate of a tropical cyclone (TC) making landfall near the delta region. A spun-up TC is placed 135 km from a north-south oriented coastline. Idealized triangular-shaped deltas, pointing to the west with length 150 km and a river mouth size of 100 km, and with roughness and moisture availability the same as the sea specified in the experiments are inserted along the coastline. All deltas are within 300 km from the TC center at landfall. Results suggest that the TC in the control (CTRL, i.e. without a delta) experiment 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. In addition, the TCs in all the delta cases also have tracks that differ from that of the CTRL. The asymmetric flow patterns due to the differential distribution of roughness and dryness of the land surface during landfall are also different between the CTRL and the delta cases. This in turn alters the potential vorticity tendency distribution hence the TC motion. These results suggest that numerical predictions of TC landfall should have a good representation of the land configuration in the model.