At the beginning of this month, hurricane researcher Brian McNoldy was sitting at his desk at the University of Miami looking at the different weather models for storms in the Pacific. Then, on November 3, the U.S. Navy's Joint Typhoon Warning Center in Hawaii issued a tropical cyclone formation alert. "You could tell early on that this had the potential to be big," McNoldy says. "Not 195 mph big, but big."
Indeed, the stage had been set for a slate of powerful storms in the Pacific. Haiyan, which blew across the Philippines early this morning, was the 5th category 5 typhoon in the Pacific so far this season. While damage details are still emerging, Haiyan will go down as one of the most powerful storms in history, packing winds estimated at 195 miles per hour and driving a powerful storm surge that flooded low-lying cities. An estimated 750,000 people were evacuated as the storm approached.
To put it in perspective, the Atlantic hasn't seen a category five hurricane since Felix in August of 2007, according to Jeff Masters, former hurricane hunter and director of meteorology at Weather Underground. Sandy, by comparison, was a category 2 storm as it approached the shores of New Jersey in October of 2012.
What's behind these powerful storms? The first key ingredient is warm ocean water, which fuels storms as heat transfers from the surface to higher altitudes. At the moment, the water temperature where Haiyan formed is a balmy but typical balmy 86 degrees Fahrenheit. This area of the western Pacific, some 3000 miles west of Hawaii, is the breeding ground for Pacific storms that then continue moving eastward towards Australia and Asia.
Another important factor is that the water is also warm below the surface. This means that as the storm grew and churned up the sea, there was no cold water emerging from below to weaken its power, even as Haiyan and its category-five cousins crossed thousands of miles of open water on their path towards landfall in Southeast Asia.
The final ingredient for a category five super typhoon is low wind sheer. "It's the difference between the wind speed at the surface and higher altitudes," says McNoldy. "With Haiyan there was very little wind shear, so the storm was moving together at both low and high levels. That's part of the reason the typhoon had such a classic shape to it."
While these three critical ingredients gave Haiyan its power, similar conditions have been stable in the Pacific Ocean for several weeks now. Of the more than 20 major storms to have hit the Philippines so far this season, most didn't posses anywhere near the power and force of Haiyan—despite surprisingly similar conditions. "This is where science doesn't have the answers yet," says McNoldy. "Why does one typhoon generate 195-mph winds, while another one with the same essential ingredients does not? We have absolutely no idea."