A numerical study of the effect of island terrain on tropical cyclones

A triply nested, movable mesh model was used to study the behavior of tropical cyclones encountering island mountain ranges. The integration domain consisted of a 37 degrees -wide and 45 degrees -long channel, with an innermost mesh resolution of super(1) / sub(6) degrees . The storms used for this study were embedded in easterly flows of similar to 5 and similar to 10 m sec super(-) super(1) initially. Realistic distributions of island topography at super(1) / sub(6) degrees resolution were inserted into the model domain for the region of the Caribbean, including the islands of Cuba, Hispaniola, and Puerto Rico; the island of Taiwan; and the region of Luzon in the northern Philippines. It was found that the islands affected the basic flow as well as the wind field directly associated with the storm system. The combination of these effects caused changes in the track and translational speed of the storm. In particular, in the case of the 5-m sec super(-) super(1) easterly flow, the storm accelerated and veered to the north well before reaching Taiwan. For the other island distributions, the northward deflection of the track and the increase of translational speed occurred near and over the islands. After landfall, the surface pressure underwent rapid filling. As the tropical cyclone passed over Hispaniola, the surface low continued to move along with the upper level vortex as it traversed the mountain range, while over Luzon, it became obscure before re-forming on the lee side slope of the mountain. In the case of Taiwan and the 10-m-sec super(-) super(1) easterly zonal flow, secondary surface lows developed behind the mountain range. The upper level vortex in this case became detached from the original surface low and eventually coupled with a secondary one. The intensity changes of the storm near and over the islands were strongly related to the latent energy supply and the vertical coherence of the storm system. Advection of dry air from near or above the mountaintops into the storm area caused significant weakening of all the storms moving with the weaker easterly flow. Storms leaving Hispaniola and moving over open sea quickly reintensified as their vertical structure remained coherent. Storms leaving Luzon were disorganized and did not reintensify until several hours later, when the vertical coherence of the systems was reestablished. Although these experiments were performed for an idealized experimental design and basic flow, many observed storms h