for National Geographic News
Hurricane Bill became the first hurricane of the 2009 Atlantic season today by skirting disruptive African air currents.
By Wednesday, Bill will likely be a major hurricane, thanks to warm water and minimal upper-level winds, which can disrupt hurricanes, said Jeff Masters, director of meteorology for the Weather Underground Web site.
With a minimum of Category 3 status, major hurricanes have sustained winds of at least 110 miles (177 kilometers) an hour.
Hurricane Bill: Projected Path
Currently churning above the middle of the Atlantic just north of the Equator, Hurricane Bill is moving north-northwest. The U.S. National Hurricane Center tentatively puts the Bill in the vicinity of Bermuda by Saturday morning.
As of mid-day Monday, though, Hurricane Bill's projected path is hazy, since the storm is so far out to sea, said hurricane specialist Michael Brennan of the National Hurricane Center office in Miami.
"At this point, it looks like it will stay north of the Lesser Antilles [in the Caribbean]," Brennan said. The Lesser Antilles islands arc along the eastern edge of the Caribbean Sea from the Virgin Islands south to Trinidad and Tobago and west to Aruba (regional map).
"But it's maybe too early to say whether it will affect the U.S."
Hurricane Bill is part of an unusual sudden flurry of activity that produced tropical storms Ana, Bill, and Claudette within a 33-hour period.
El Niño conditions had kept a lid on Atlantic tropical storm formation since the hurricane season began on June 1. El Niño—an unusually warm flow of Pacific waters that sometimes forms off the northern coast of South America— creates upper-level winds that can disrupt hurricane formation in the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico.
How Hurricane Bill Beat the African Curse
Like any hurricane, Bill owes its strength to warm, moist air. The storm formed far enough south in the Atlantic to escape the dry, hurricane-stifling air that wafts westward from Africa's Sahara desert (map).
(Related: "Hurricane Secrets May Be Revealed by African Thunderstorms.")
Over the Atlantic, there's a dramatic difference between air currents to the north and south of latitude 20 degrees north. Air north of that latitude is Saharan. The humid air to the south is from African rain forests.
"It's always a delicate matter when storms are forming off Africa as to how much dry air they'll have to deal with," Weather Underground's Masters said. "If they form too far to the north, they'll struggle.
"Bill formed a little farther south and didn't have any trouble."
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