How Irma became Irma: A monster storm six months in the making

Irma has ripped a path of misery through the Caribbean and is aiming at Florida, but the first seed for its monster size and force was planted on the other side of the world more than six months ago.It happened innocently enough, when a widely anticipated El Nino failed to materialise over the Pacific Ocean. In time, that cleared a path for a hurricane to form in the Atlantic that grew to the size of the state of New York with winds topping 185 miles per hour.“The odds of getting an Irma in an El Nino year are really low,” said Phil Klotzbach, lead author of Colorado State University’s seasonal hurricane forecast. Peruvian fishermen back in the 1600s gave the recurring meteorological event its name, Little Boy or Christ Child in Spanish, when they noticed the tropical Pacific warming around Christmas in some years.El Nino occurs when the Pacific heats up and flusters the atmosphere, setting off a chain reaction that causes wind shear across the Atlantic. Shear is wind blowing in different directions or speeds at various altitudes, and it can be Kryptonite for hurricanes. As powerful as they are, tropical cyclones have delicate structures. Shear can tear them apart. A budding storm can’t get started and an established storm can’t get strong.Beasts like Irma churn out from one of the tropical waves that slide off the coast of Africa. These troughs of low pressure, sometimes just a ragged collection of thunderstorms, begin to roll off the continent in late spring. That’s a reason the Atlantic hurricane season runs from June 1 to November 30.The waves are the seedlings, said Rick Knabb, hurricane expert at the Weather Channel in Atlanta and until last year director of the National Hurricane Center in Miami. “Hurricanes don’t just pop out of nowhere.”They need warm water for fuel, which this summer has provided. The water in the tropical Atlantic, from the Leeward Islands to Cape Verde, has been about 2 degrees Fahrenheit (1 Celsius) higher than normal in the area where Irma is prowling, Klotzbach said.Irma also got a boost from a deep, moist atmosphere. Earlier in the summer in the Northern Hemisphere, dry air usually blows off Africa’s Sahara Desert, sometimes carrying dust that can be seen from space and can give the Miami sky a hazy cast. That wraps into storms, sapping them of strength.“Around August 20, the dust tends to die down,” Klotzbach said. And then hurricane season begins, building to its September 10 statistical peak, according to the National Hurricane Center.All the ingredients combined to create one of the strongest storms ever to rise out of the Atlantic Ocean and the most powerful to form outside of the Caribbean and the Gulf of Mexico.For those keeping score, however, Irma still can’t be called the most intense ever recorded in the Atlantic. That honour is held by 1980’s Allen, which packed winds of 190 miles per hour.But the season isn’t over. Normally, the 11th named storm doesn’t show up until November 23, according to the hurricane centre. Irma is No 9, and 10 and 11, Jose and Katia, are already here.Tropical Atlantic storms started getting women’s names in 1953As hurricanes Irma, Jose and Katia churn through the Atlantic, it’s no coincidence that their names run in alphabetical order, Bloomberg said. It’s by design thanks to the National Hurricane Center, which began naming Atlantic storms in 1953. Before that, systems were designated by places or events. One Atlantic storm that ripped off the mast of a boat named Antje became known as Antje’s hurricane. Distinctive storm names facilitate communications between coastal bases, inland stations and ships at sea, according to the World Meteorological Organisation, which eventually took over the job. Men’s names were added in 1979. Names can be reused, though some are retired if there is a large loss of life or extreme property damage. There are no storms that begin with Q, U, X, Y or Z. In 2005, the organisation ran through its list of names and began using letters from the Greek alphabet.