The Science Behind Hawaii’s Double Hurricane
Having two cyclones in the ocean is not rare, but when they get too close to each other things can get crazy
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Early this week, Hawaii was bracing for the arrival of Hurricane Madeline, which passed south of the island last night as a tropical storm. If Madeline had made landfall, it would have been a first; a hurricane has never made landfall on the island of Hawaii since records began in 1949, but it has experienced five prior tropical storms, according to Jason Samenow at The Washington Post.
There is something even more interesting about Madeline. She has a big brother, hurricane Lester, which peaked as a Category 4 storm, following 1,000 miles behind in her wake. As Lester has approached the Hawaiian islands, it has significantly weakened but is still violently swirling with sustained winds of 130 miles per hour, according to a recent NOAA report.
The NASA image (and recent footage from space, below) of the two storms is stunning: the spiral clouds lined up over the ocean like two turntables of destruction. And though double hurricanes are rare, they are not unheard of. Even more, when two tropical cyclones, the technical term for hurricanes and tropical storms, get close to one another a whole new set of physics can take effect.
Hurricanes form when the top 165 feet or so of ocean water reaches 80 degrees or higher. At this high temperature, the surface water evaporates and the rising water vapor forms a cloud column. Winds circulate around the column, and over time they spread out, spinning with ever greater speed. The spread comes from heat that is released at the top of the column, which increases the overlying air pressure. As this process continues and strengthens, the storm can become a tropical depression, tropical storm and eventually a hurricane.
It’s not unusual for multiple storms to form in one ocean, especially if conditions are right. “[They] can occur close together in any ocean basin,” Chris Davis, senior scientist with the National Center for Atmospheric Research in Boulder tells Jane Lee at National Geographic. “They can form farther apart and move closer together during their lifetime.”
That seems to be the case with Madeline and Lester. Hawaii faced a similar threat in August of 2014 when hurricanes Iselle and Julio looked like they were taking dead aim at the islands. Iselle did make landfall after weakening into a moderate tropical storm. Hurricane Julio also weakened and passed to the north of Hawaii.
Other areas haven't been so lucky, and double storms have made landfall several times. In February 2015, tropical cyclones Lam and Marcia pummeled Australia’s northern coast, making landfall within six hours of one another and destroying 350 homes. In August 2004, tropical storm Bonnie hit the Florida panhandle before Category 4 Hurricane Charley hit southwest Florida in August 2004. In 1906, hurricanes dubbed Storm 9 and Storm 8 also hit Florida within 12 hours of each other.
But things get interesting when tropical cyclones get within 800 miles of each other. When this happens, the storms create a Fujiwhara effect, named after the early 20th century Japanese meteorologist who discovered the phenomenon. The effect causes the two storms to begin rotating around a fixed center of mass between them and can dramatically shift the two rotating bodies off their current course.
There are many examples of storms dancing around each other due to this effect. In 2004, Hurricanes Lisa and Karl tangoed briefly in the eastern Atlantic, and in 1976 Hurricanes Emmy and Frances also took a spin together.
But the Fujiwhara effect had its biggest impact on Superstorm Sandy. When that weather system was still a hurricane in the Atlantic, Adam Sobel at Climate Central wrote that it began interacting with a large winter storm system over the eastern U.S. It began to rotate around a fixed point with that storm, causing Sandy to make its hard left turn into the Jersey coast instead of staying farther out to sea.
Lester and Madeline did not get close enough to to begin the Fujiwhara dance. But if they had, it would've be good news. Jeff Masters at Weather Underground writes that a Fujiwhara interaction would likely have sent Madeline south of the island chain and Lester hurtling away to the north.