Don’t expect them all to turn north.
When Danielle was a hurricane, it curved well short of the U.S. coastline. Earl — now a Category 4 powerhouse — might do so as well. But future storms may not follow suit.
The basic steering currents guiding Danielle, Earl and newly formed Tropical Storm Fiona are sure to change in just a matter of days. Already, atmospheric forces have pushed Earl farther west than Danielle, making it a possible threat to the mid-Atlantic or northeastern U.S. later this week.
“The environment is constantly evolving and changing,” said James Franklin, top hurricane specialist at the National Hurricane Center in Miami-Dade County.
Danielle, downgraded to a tropical storm on Monday night, was racing into the North Atlantic to die while Earl was pounding the British Virgin Islands with heavy rains, howling winds and battering waves.
Earl was projected to be 600 miles east of Florida on Wednesday, bringing a high risk of rip currents this week.
By Thursday, Earl was expected to reach near-Category 5 status and come perilously close to the Outer Banks of North Carolina. It could be within 300 miles of New York City on Friday, possibly as a Category 2 hurricane. The cone of uncertainty includes much of the Northeast, including Vermont, New Hampshire and Maine.
For now, Fiona is forecast to follow a path similar to Earl’s, arriving well east of Florida by the weekend, far enough away that it likely will have little or no impact.
One of the main atmospheric features that guided Danielle and Earl to the north is the Bermuda High, a vast area of high pressure that generally sits over the western Atlantic. Both systems followed the high’s western edge.
But Franklin noted the Bermuda High is one of several steering mechanisms, including other high pressure systems, low pressure areas and wind patterns at different latitudes.
He said each storm is directed by its own particular set of atmospheric conditions, and they cannot be predicted with any certainty more than four or five days in advance.
“In several days, there will be another atmospheric setup,” he said.
For instance, Danielle found an alley between the Bermuda High and another high-pressure area over the U.S. East Coast. Danielle was then pulled to the northeast by a low-pressure area between the two high pressure systems. Earl is expected to eventually find the same alley and curve northeast.
The low-pressure system, however, is moving to the east, allowing high pressure to build back across the Atlantic.
“That’s going to force Earl to move a little farther west than Danielle,” Franklin said. “We don’t know how far west it will get.”
Future storms also might be directed farther west, he said.
There have been seasons where the same basic steering currents remain in place for several weeks.
In 2004, the Bermuda High drove Hurricanes Charley, Frances, Ivan and Jeanne into Florida’s shoreline, all within 48 days.
High pressure also pushed a few systems to the west in 2005, including Hurricanes Dennis, Katrina and Rita, all of which struck the U.S. coast.
“Occasionally, you’ll see seasons with semi-persistent patterns,” Franklin said.
Hurricane center spokesman Dennis Feltgen said it’s possible for one tropical system to influence the strength and direction of another, although that is not expected to be the case with the current storms.
“The outflow from one storm can get on top of another storm and help weaken it,” he said. “And a bigger storm can absorb the remnants of another storm.”
He added that one active hurricane will never merge with another.
“It’s a physical impossibility,” he said. “They actually repel each other.”
The peak of hurricane season, Sept. 10, is less than two weeks away and forecasters predict the tropics will be highly active.
“It’s just time be vigilant,” said hurricane specialist Eric Blake.