HONOLULU — Hawai‘i has been largely free from Hurricanes in the recent past, with only two having made landfall in more than 30 years. Kaua‘i is the island that has suffered the most, with Hurricane Iwa in 1982 causing more
HONOLULU — Hawai‘i has been largely free from Hurricanes in the recent past, with only two having made landfall in more than 30 years.
Kaua‘i is the island that has suffered the most, with Hurricane Iwa in 1982 causing more than $250 million in damages, a record for Hawai‘i at that time, and Hurricane ‘Iniki in 1992, pushing the record to $2 billion.
Now, a study headed by a team of scientists at the International Pacific Research Center at the University of Hawai‘i at Manoa, shows that Hawai‘i could see a three-fold increase in tropical cyclones by the last quarter of this century.
The study, which appeared in the May 5 online issue of Nature Climate Change, though, leaves open the question, how worried Island residents should get.
“Computer models run with global warming scenarios generally project a decrease in tropical cyclones worldwide. This, though, may not be what will happen with local communities,” lead author Hiroyuki Murakami said in a UH news release Tuesday.
To determine whether tropical cyclones will become more frequent in Hawai‘i with climate change, Murakami and climate expert Bin Wang at UH Manoa Meteorology Department joined forces with Akio Kitoh at the Meteorological Research Institute and the University of Tsukuba in Japan.
The scientists compared in a state-of-the-art, high-resolution global climate model the recent history of tropical cyclones in the North Pacific with a future — years 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,” Murakami said. “From 1979 to 2003, both observational records and our model document that only every four years on average did a tropical cyclone come near Hawai‘i. Our projections for the end of this century show a two-to-three-fold increase for this region.”
The main factors responsible for the increase are changes in the large-scale moisture conditions, the flow patterns in the wind, and in surface temperature patterns stemming from global warming.
Most hurricanes that might threaten Hawai‘i 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 3,000 miles to Hawai‘i, they usually fizzle out due to dry conditions over the subtropical central Pacific and the wind shear from the westerly subtropical jet.
Surprisingly, even though fewer tropical cyclones will form in the eastern Pacific in Murakami’s future scenario, we can expect more of them to make their way to Hawai‘i.
The upper-level westerly subtropical jet will move poleward so that the mean steering flow becomes easterly.
Thus, storms from Baja California are much more likely to make it to Hawai‘i. Furthermore, since the climate models also project that the equatorial central Pacific will heat up, conditions may become more favorable for hurricane formation in the open ocean to the south or southeast of Hawai‘i.
