Modeling of topographic wind speed effects in Hawaii

Terrain or topographic amplification of wind speed has been a significant contributing factor in the past hurricane loss experiences of Hawaii and various islands in the Pacific region, such as Guam and American Samoa. In Hawaii, where the real terrain is very complex, the actual magnitude and extent of speedup can be quite different from current building code formulas. To address this issue pertinent to both loss estimation and structural design in Hawaii, regional scale models of selected developed portions of the Hawaiian Islands have been constructed and tested in a boundary-layer wind tunnel to determine wind velocity accelerations and decelerations due to topographic influence over a grid of data acquisition locations. Influences of terrain, directionality, channeling, and topographic features have been identified. Wind-tunnel test data were utilized to develop empirical models for peak, and mean wind speed-up based on spatially weighted parameters derived from a Digital Elevation Model raster grid of terrain and relevant categorical landform variables. A geographic information system was then used to provide detailed contouring of the wind flow speed-ups. This provided a micro-zoned mapping of directional wind speed-up factors relative to the speed at a flat open coastal site.