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Global warming: More hurricanes in Hawaii?

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Hurricane Iniki reached Kauai in September 1992 as a Category 4 storm, with winds up to 140 mph.

Study projects two to three times as many storms by the end of the century

By Summit Voice

SUMMIT COUNTY — Large scale shifts in hemispheric circulation patterns and ocean temperatures are likely to steer more hurricanes toward the Hawaiian Islands in coming decades.

A poleward shift of the subtropical jet stream and warmer temperatures over the equatorial central Pacific will combine to make the storms two to three times as likely by the last quarter of the century, according to scientists with the International Pacific Research Center, University of Hawaii at Manoa.

Our finding that more tropical cyclones will approach Hawaii as Earth continues to warm is fairly robust because we ran our experiments with different model versions and under varying conditions. The yearly number we project, however, still remains very low,” said study co-authorBin Wang, a climate expert at the university.

Most climate models predict a general decrease in tropical cyclones worldwide, but the Hawaiian Islands could be more susceptible to storms that do form off the southwest coast of Mexico.

The University of Hawaii researchers teamed up with Akio Kitoh at the Meteorological Research Institute and the University of Tsukuba in Japan to model the recent history of tropical cyclones in the North Pacific with a future (2075–2099) scenario, under which greenhouse gas emissions continue to rise, resulting in temperatures about 2 degrees Celsius higher than today.

“In our study, we looked at all tropical cyclones, which range in intensity from tropical storms to full-blown category 5 hurricanes. From 1979 to 2003, both observational records and our model document that only every four years on average did a tropical cyclone come near Hawaii. Our projections for the end of this century show a two-to-three-fold increase for this region,” said Murakami.

Most hurricanes that might threaten Hawaii now are born in the eastern Pacific, south of the Baja California Peninsula. From June through November the ingredients there are just right for tropical cyclone formation, with warm ocean temperatures, lots of moisture, and weak vertical wind shear. But during the storms’ long journey across the 3000 miles to Hawaii, they usually fizzle out due to dry conditions over the subtropical central Pacific and the wind shear from the westerly subtropical jet.

The study appeared online in the May 5, 2013, online issue of Nature Climate Change.

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