Anniversary for 'seedling' that became Sandy
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Friday is not exactly superstorm Sandy's birthday, but still, a year ago on Oct. 11, a tropical wave seen primarily as "Sandy's origin" left the west coast of Africa, according to a February report from the National Hurricane Center.
Typically two to three such easterly waves form over the Atlantic at any one time from mid-August to mid-October, "but most of these low pressure troughs do not develop into tropical storms," said Brian Colle, professor of atmospheric sciences at Stony Brook University.
As with others, the "seedling" that became Sandy "was carried across the ocean by the easterly trade winds," he said.
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After a seven-day journey, on Oct. 18 "the wave entered the eastern Caribbean Sea. . . with only a weak wind shift and some showers noted in the Windward Islands," the hurricane center report said.
By Oct. 21, "the circulation of the low became well defined" around 200 miles south of Jamaica, the report said, forming a tropical depression the next day and tropical storm six hours later.
It's at that tropical depression stage that forecasters "really start keeping score," Colle said, and that's the day -- Oct. 22 -- that he sees as the anniversary of the storm's formation.
The storm was christened Hurricane Sandy on Oct. 24, centered just south of Kingston, Jamaica, and was deemed a major hurricane the next day, the report said. Sandy went on to intensify, diminish, regain strength and head northeast parallel to the U.S. coast.
As bad luck would have it, a high pressure pattern in the North Atlantic would block it from turning east and out to sea, and a low pressure system approaching over land would help it "re-intensify" and head northwest, toward the mid-Atlantic states, the report said.
To make "a bad thing even worse," Colle said, then superstorm Sandy and its massive storm surge arrived in New York just in time for high tide.
And that would be a date that many will remember -- Oct. 29, 2012.