Influence of topography on the track and intensity of tropical cyclones
Tropical cyclones, deriving their energy from surface evaporation of warm ocean water, tend to diminish over land. Mountainous terrain, in particular, generally weakens hurricane circulations. Additionally, the intensity and track can change as the change in moisture supply alters the location and strength of the deep convection. Geerts, et al. (2000) documents the changes in Hurricane George as it moved over the mountainous island of Hispaniola. May et al. (2008) used weather radar to gather detailed observations of Tropical Cyclone Ingrid as the storm passed parallel to and close to the coastline near Darwin, Australia. They noted significant changes to the tangential wind field as the storm passed over a narrow region of open ocean. Chan and Liang (2003) used the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) to simulate landfall of a hypothetical vortex. They found that while the main effect on the storm came from the modification of the surface latent heat flux; lack of moisture changed where the convection appeared in the storm, by modifying the moist static stability of the atmosphere. Farfan and Cortez (2005) used the MM5 to investigate Hurricane Marty as the storm moved over the Baja Peninsula and into the Gulf of California. Flattening of the mountains in one model run allowed Marty to not be deflected into the Gulf, suggesting that the mountains acted as a physical barrier to the storm movement. Ramsay et al. (2008) used the MM5 to investigate the influence of mountains on Hurricane Larry as the storm made landfall. They did two model runs, one with real topography, and one with topography set to zero. The mountains played a significant role in the modification of the wind field and in the track as Larry moved inland.
The hurricane season of 2010 included storms that passed near land and storms that passed over land. Hurricanes Alex, Karl, and Richard all passed over the Yucatan Peninsula without dying. Tropical Storm Nicole moved right over Cuba before expiring south of Florida. Hurricane Paula grazed the coast of Nicaragua, curved by the Yucatan Peninsula, and then moved along the north coast of Cuba, ending near the same point Nicole ended at, just south of Florida. Finally, Hurricane Tomas, after moving westward for nearly a week, recurved south of Haiti, and moved through the narrow strait between Haiti and Cuba, then continuing on to the northeast.
Using the NCAR Advanced Research Hurricane WRF model, storm simulations will be examined to determine the role the topography played in a) the storm track and b) the deep convection in the core. Three runs, one with the real topography, and one with flattened topography, and one with all ocean will allow careful diagnosis of the influences the topography may be having on these tropical storms, at least as far as a numerical model can show. The simulations will be made using a small Linux cluster. Runs with 2 nested domains have already been made (30 and 10 km grid spacing, see the Figure for an example from the 30 km grid.); a third and perhaps fourth nest will be added at 3.3 and 1.1 km to resolve the mesoscale details.
References:
Chan, Johnny C. L., Xudong Liang, 2003: Convective Asymmetries Associated with Tropical Cyclone Landfall. Part I: f-Plane Simulations. J. Atmos. Sci., 60, 1560–1576.
Farfán, Luis M., Miguel Cortez, 2005: An Observational and Modeling Analysis of the Landfall of Hurricane Marty (2003) in Baja California, Mexico. Mon. Wea. Rev., 133, 2069–2090.
Geerts, Bart, Gerald M. Heymsfield, Lin Tian, Jeffrey B. Halverson, Anthony Guillory, Mercedes I. Mejia, 2000: Hurricane Georges's Landfall in the Dominican Republic: Detailed Airborne Doppler Radar Imagery. Bull. Amer. Meteor. Soc., 81, 999–1018.
May, Peter T., J. D. Kepert, T. D. Keenan, 2008: Polarimetric Radar Observations of the Persistently Asymmetric Structure of Tropical Cyclone Ingrid. Mon. Wea. Rev., 136, 616–630.
Ramsay, Hamish A., Lance M. Leslie, 2008: The Effects of Complex Terrain on Severe Landfalling Tropical Cyclone Larry (2006) over Northeast Australia. Mon. Wea. Rev., 136, 4334–4354.
Figure showing Hurricane Alex, just south and east of the Yucatan Peninsula, at 12 UTC, June 26, 2010, from an AHW simulation begun at 00 UTC, June 24, 2010.