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CRAMP: North East Trade Wind Waves

NE Trade Wind Waves are a dominant factor controlling reef community structure on the NE facing Hāmākua Coast (Island of Hawai‘i). Photo by Paul Jokiel at Laupāhoehoe.

NE Trade Wind Waves prevail throughout the year in Hawai‘i (although they may be absent for days or even weeks at a time), and reach maximum intensity between spring and fall. These winds are the result of the semi-permanent Eastern Pacific (EASTPAC) High which is usually centered to the north and east of the Hawaiian Islands. The average frequency of the NE trades varies from over 90% during the summer to less than only 50% in January. The Northeast Trade Winds typically diminish during the night and gradually increase throughout the morning to maximum wind speeds in the afternoon. Increased wind speed causes an increase in the size of wind-driven waves. Offshore wind-generated wave heights of 4 to 12 feet are typical with periods of only 5 to 8 seconds. These offshore waves break and dissipate along the north and easterly shores of the Hawaiian Islands. NE Trade Wind waves generally arrive from the NE (45°), but direction can vary between 0° and 90°. The high islands are a barrier to the surface winds, which can greatly increases trade wind velocity as the air funnels through gaps between the islands (Flament et al.1996). This phenomenon creates very choppy seas and modifies currents in channel areas, especially between the Islands of Hawai‘i, Maui and Moloka‘i.

References:

Flament et al.1996

 

 

Last Update: 04/21/2008

By: Lea Hollingsworth

Hawai‘i  Coral Reef Assessment & Monitoring Program

Hawai‘i  Institute of Marine Biology

P.O. Box 1346

Kāne‘ohe, HI 96744

808-236-7440 phone

808-236-7443 fax

email: jokiel@hawaii.edu