Hawaiian Northeast Trade Winds Are Decreasing
October 15, 2012

Analysis Confirms That Trade Winds Over Hawaii Are Shifting

April Flowers for redOrbit.com - Your Universe Online

University of Hawaii at Manoa (UHM) researchers have noticed an increased frequency of the eastern trade winds and a decrease in frequency of the north east trade winds over the last 40 years. The study, published in the Journal of Geophysical Research, analyzed 37 years of wind speed and direction, and sea level pressure data from land-based weather stations, buoys and reanalysis data.

For example, the northeast trade winds occurred 291 days per year at the Honolulu International Airport 37 years ago. Today, they only blow 210 days a year.

Because they affect wave height, cloud formation, and precipitation over areas of the region, the northeast trade winds are very important to the Hawaiian Islands. Without these winds, the air becomes dormant and inclement weather develops.

Pao-Shin Chu, Meteorology Professor and Head of the Hawaii State Climate Office, explained that a lack of these winds could fundamentally change the overall climate of the Hawaiian Islands, as the trade winds are the primary source of moisture for rain.

"We have seen more frequent drought in the Hawaiian Islands over the last 30 years," he noted. "Precipitation associated with the moisture-laden northeasterly trades along the windward slopes of the islands contributes much of the overall rainfall in Hawaii."

Over the past year, nearly 50% of land in Hawaii has suffered some degree of drought, according to the National Drought Mitigation Center's State Drought Monitor.

The findings of this study, along with Chu's 2010 study, are the first to show changes in trade wind frequencies. Previously, research into the trade winds has been limited to changes in wind intensities.

"In 2010, we only studied the trade wind changes at four major airports in Hawaii (Honolulu, Kahului, Hilo, and Lihue). In the current paper, we expanded our study to include four ocean buoys in the vicinity of Hawaii and a large portion of the North Pacific," Chu commented.

Chu and his group intend to focus future studies on understanding the dynamics of rainfall and trade winds to estimate future patterns using model simulated data.