Hurricane Hazards Mitigation

Hurricanes are one of the most devastating natural disasters in the U.S. Hawaiʻi is vulnerable to hurricanes between June and November, when the sun heats up the ocean surface temperatures enough to produce strong storms with winds in excess of 74 mph. Because of the Coriolis effect, these strong storms rotate in a circular fashion, and hurricanes can grow to hundreds of miles across.

A hurricane develops gradually from a smaller storm system. A tropical depression is an organized system of clouds and thunderstorms with defined circulation and maximum sustained winds of 38 mph or less. This weather system can strengthen and become a tropical storm, with maximum sustained winds of 39 to 73 mph. In turn, a tropical storm can grow into a hurricane, an intense tropical weather system with a well defined circulation and maximum sustained winds of 74 mph or higher.

Each year, several hurricanes develop that approach Hawaiʻi, but fortunately most veer off or dissipate. However, hurricanes have struck Kauaʻi in 1982 and 1992, and the Big Island was apparently hit in the late 1800’s according to historical descriptions.

Hurricanes produce storm surge, rain, and wind. Storm surge results when the low-pressure storm system raises sea level—as much as several feet at the leading edge of a hurricane—so that waves come much further inland than they normally would. This causes flooding and erosion of coastal areas. Rain can cause severe flooding in the upland areas and, on steep slopes, produce mud and debris flows that devastate everything in their path. Strong winds can damage utility lines and poles, tear poorly attached roofs from homes, and turn smaller debris into projectiles that damage homes and cause injuries and loss of life.