From the ABC 7 Weather team

Hurricane Irene path: Why is the East Coast a target?

August 25, 2011 - 04:30 PM
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What is a trough, and what does it have to do with Irene?

Greetings! John Metcalfe, your everyday weather blogger, is on vacation. My name is Jeremy Binckes, and I have dabbled in weather. I'm happy to be filling in, considering that Metcalfe will be missing one of the more awesome weather stories of the past decade.

The most recent predictions are showing that Hurricane Irene has Cape Hatteras in its sight. Early projections (Monday or Tuesday) showed that the storm would strike North Carolina then curve off to the east. However, the most recent projections are showing that Irene is likely to hug the Eastern Seaboard — a straight-line projection that's exceptionally rare. It comes down to a matter of timing.

The arrival of Irene is timing perfectly with a trough — an elongated stretch of low pressure — stretching south-to-north along the coast. This stretch of low pressure provides a path of least resistance for the storm to travel. More importantly, it prevents the strong westerly winds from kicking in and pushing Irene out to sea; that's what happened to Hurricane Earl last year.

"The trough is just the actual cold front — it's interchangable — it's an area of low pressure. With this area of low pressure, tropical storms and hurricanes will follow this path," said WJLA meteorologist Devon Lucie.

"It's a very unusual situation," added meteorologist Bob Ryan. "We have upper-level steering winds which usually are strong from the west pushing to the east. This one, because there is this wave from the west, is drawing Irene up the coast."

Could the forecasts — which have already shifted west — change even more, leading to a path through the Delmarva peninsula? It is a possibility, but Ryan gives it a 20 percent chance that the storm trends west.

"Remember, it's Thursday, and the impact is Saturday night into Sunday."

The north trajectory is one half of the twin dangers of Irene, and this is reason to be a bit worried. According to the most recent reports, Irene has been delivering gusts of more than 101 miles per hour to the Bahamas, despite being more than 100 miles north of Nassau. Most hurricanes are more compact, delivering hurricane-force winds only a few miles from the center. Assuming Irene remains a Category 2 hurricane, and stays just off the East Coast parallel to D.C., the eastern parts of the region will have rather strong winds. 

"If Irene holds together as is, we can have some pretty hefty winds here in D.C.," said Lucie. "Right now, the official forecasts are calling for at least tropical storm force winds — just under Category 1 status — in parts of the metro area." Western areas, such as Loudoun County, might not see as much damage. "The metro area is on a fine line [geographically]," Lucie said. 

One thing is for certain: As Thursday turns to Friday, there will be a close eye on Irene's projected track.

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