Why Irma is so strong, and other storm questions answered
WASHINGTON— A powerful hurricane Irma is threatening millions of people in the Caribbean and Florida. Some answers to questions about Irma and hurricanes:
Where do these storms come from? Irma is a classic Cape Verde storm, which begin near the islands off the west coast of Africa.
Some of the worst hurricanes start as puffs of unstable air and storminess there and chug west, gaining strength over the warm, open Atlantic.
Another storm, Jose, has followed in Irma’s footsteps.
Some of those storms fizzle from wind shear or other weather conditions. Still others curve harmlessly north into the mid-North Atlantic and are called “fish storms.”
Storms also start in the Gulf of Mexico, like Katia, which formed off Mexico and was declared a hurricane on Wednesday.
Why are storms happening now? Hurricane season starts June 1 and ends Nov. 30. That’s usually when the water is warm enough and other weather conditions are conducive to storm formation. Hurricanes need water that’s at least 26 C. Peak hurricane season is from mid-August to mid-October with the peak being Sept. 10 or 11.
What’s an average season like? An average season produces 12 named storms, ac- cording to the National Weather Service. Wednesday’s Katia is the 11th this season.
Storms get names when winds reach 63 kilometres/hour.
The average season produces six hurricanes, and three of those become major at 180 km/h winds or higher.
So far this year, there have been six hurricanes: two major ones, Harvey and Irma; two new ones Wednesday, Katia and Jose; and Franklin and Gert.
Did forecasters see this busy year coming? Yes. In May, the weather service predicted a 70-per-cent likelihood of 11 to 17 named storms with five to nine becoming hurricanes.
They predicted two to four major hurricanes. In early August, it was changed to a 60-per-cent chance of 14 to 19 named storms, five to nine hurricanes and two to five major hurricanes.
Why is Irma so strong? Hurricanes use warm water as fuel. Irma has been over water that is 0.7-1C warmer than normal. And that warm water goes deeper than usual. High altitude winds, which can fight or even decapitate storms, are not strong, also helping Irma.
While over the open Atlantic Ocean on Tuesday, Irma’s almost 300 km/h winds set a record for that region. In the entire Atlantic, Caribbean and Gulf of Mexico, only Hurricane Allen in 1980 was stronger, with winds of 305 km/h recorded. Others with near 300 km/h winds: a 1935 Florida storm, 1988’s Gilbert and 2005’s Wilma.
Is this global warming? Scientists take weeks or months to conduct intricate studies, using computer simulations, to see if a storm was worsened by man-made climate change.
There have been a limited number of hurricanes since record-keeping began in 1851, which makes it difficult to do robust statistical analyses. However, scientists say future global warming would make some of the worst storms stronger and wetter and recently have linked climate change to rapid intensification of storms.
There’s been debate over whether global warming means more storms, but the “stronger and wetter” is generally accepted by scientists.