National Geographic News
An infrared image of Hurricane Irene.
Hurricane Irene churns over the Caribbean Wednesday in an infrared satellite picture.

Image courtesy NOAA

Willie Drye in Plymouth, North Carolina

for National Geographic News

Published August 25, 2011

The exact times, places, and intensities of Hurricane Irene's predicted U.S. landfalls are still ripe for revision, but according to meteorologist Keith Blackwell, at least one thing is certain: "It's looking bad." And the moon is at least partly to blame for that cloudy outlook.

(Also see "Hurricane Irene to Cause One of Largest Power Outages?")

Current forecasts suggest Irene will likely make landfall as a major hurricane on North Carolina's Outer Banks barrier islands this weekend, bringing damaging winds and serious flooding to coasts from North Carolina to New England.

Hurricane Irene's center is "likely to go through the Outer Banks and rake the coast all the way up—Virginia, Delaware, Maryland, New Jersey—all the way up to New England," said Blackwell, of the University of South Alabama's Coastal Weather Research Center.

"Long Island looks like it's really going to be in trouble."

However, Jack Beven, a hurricane specialist at the National Hurricane Center in Miami, pointed out that the margin of error for predicting hurricane landfall sites three days out is 150 miles (240 kilometers). This means that Hurricane Irene's actual landfall could be that far east or west of the current predicted hurricane track.

(Watch hurricane videos.)

Irene Now a Major Hurricane

As of 2 p.m. Thursday, Hurricane Irene's eye was passing over the northern Bahamas and moving northwest at about 13 miles (21 kilometers) an hour.

Irene's strongest winds around its eye were 115 miles (185 kilometers) an hour, making Irene a Category 3 hurricane on the Saffir-Simpson scale, which rates hurricanes from 1 to 5, based mainly on wind speeds.

With winds of 111 to 130 miles (179 kilometers to 209 kilometers) an hour, a Category 3 storm is considered to have crossed the threshold into "major hurricane" status.

By Friday morning, Irene will likely be a Category 4 hurricane—a storm with wind speeds between 131 and 155 miles (211 and 249 kilometers) an hour—according to the National Hurricane Center.

The hurricane-center forecast predicts that Irene will weaken some as it approaches Cape Lookout, North Carolina, but will be at least a Category 3 when the storm touches the Outer Banks late Saturday morning or early Saturday afternoon.

(Get our tips on hurricane preparedness.)

Blame It on the Moon?

Meteorologist Jeff Masters, director of the Weather Underground website, said flooding caused by Hurricane Irene could be worse than usual, because the storm will be making landfall during a new moon.

During new and full moons, the sun, Earth, and the moon are arranged in a straight line, with the sun and moon intensifying each other's gravitational pull on Earth. The result is more severe tidal fluctuations—low tides are lower than usual, but more to the point, high tides are higher.

Due to these so-called spring tides ("spring" in the sense of jumping), any town that sees the hurricane pass by during one of the two daily high tides is especially in danger of heavy flooding due to storm surges—for example, if Atlantic City, New Jersey, is hit between 7 and 8 p.m. ET Sunday, Masters said.

Storm surges are caused by a hurricane's high winds, which pile up a "mound" of water along the front of the eye as the storm moves forward. A Category 3 hurricane can push a storm surge of 9 to 12 feet (2.7 to 3.7 meters) tall ashore at landfall.

In general, Masters is especially worried about coastal New Jersey, where Hurricane Irene's storm surge could exceed ten feet (three meters). It's not so much the surge height that concerns him as the state's lack of hurricane experience.

"That area has no hurricane history whatsoever," Masters said. "They're not used to having to evacuate from hurricanes."

So far the United States has been largely spared by the 2011 Atlantic hurricane season, which lasts from June 1 to November 30. But in May the U.S. National Oceanic and Atmospheric Administration issued a busy forecast—and late-season surprises aren't unheard of.

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