Original Paper

Boundary-Layer Meteorology

, Volume 123, Issue 3, pp 463-480

First online:

Wind environment in the Lee of Kauai Island, Hawaii during trade wind conditions: weather setting for the Helios Mishap

  • John N. PorterAffiliated withSchool of Ocean and Earth Science and Technology, University of Hawaii Email author 
  • , Duane StevensAffiliated withSchool of Ocean and Earth Science and Technology, University of Hawaii
  • , Kevin RoeAffiliated withMaui High Performance Computing Center
  • , Sheldon KonoAffiliated withStatech International
  • , David KressAffiliated withIsland Air
  • , Eric LauAffiliated withNational Weather Service

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On 26 June 2003 (approximately 1030 local time) the Helios ultralight aircraft broke apart off the west coast of Kauai Island, Hawaii as it was climbing out of the Kauai wind shadow. Following the aircraft mishap, a study was carried out to understand the conditions on the day of the crash and to better characterize the wind in the lee of Kauai. As part of this effort, both aircraft measurements and numerical modelling studies were carried out. Measurements and models showed the trade wind flow was enhanced around the island creating a region of wind shear surrounding the leeside calm zone. This wind shear region was found to be vertically oriented along the south side but tilted northward with height along the northern side of the calm zone. Several other factors on the day of the crash were investigated including water vapour gradients, diurnal Island heating, and gravity waves but their possible influences on the crash could not be confirmed. While the numerical model captured the general features of the Kauai leeside winds, the orientation of the calm zone was north of the observed one.


Hawaii Helios aircraft Island wake Marine boundary layer Trade winds Wind turbulence