Irene’s Wet Legacy

Hurricane Irene was never a wind maker. Just ask any meteorologist tracking the storm since it began developing. But it was big, even for a hurricane. At one point Irene stretched over 610 miles across and hovered over half of the eastern seaboard as it roared up the U.S. Atlantic coast Saturday and Sunday. But the storm never developed a strong eye-wall so dangerous winds didn’t cause the widespread damage they could have.

Hurricane Irene was all about the water. The widespread flooding from New Jersey to Vermont places Irene in the hurricane history books. Vermont is still assessing the damage but is already blaming Tropical Storm Irene for the worst flooding in over a century. Roads in one town washed away turning the the town into an island. Babbling brooks turned into raging torrents that ripped through quaint New England villages, wiping out historic covered bridges and carrying cars, buildings and other debris away in the rapids.

Supersoaker

Rain totals are still coming in but this storm was a soaker. And soggy ground made it easier for the strong winds to knock down big trees. So far 30 people lost their lives in seven states, mostly from being crushed by trees. Dozens are still missing.

As the hurricane tracked north from the Bahamas, forecasters warned the largest number of people in U.S. history to prepare for the tropical onslaught. In all 65 million people lay in the path of the mammoth storm. Major populations centers, including Washington D.C., New York, Philadelphia and Boston were all put on high alert and evacuations began days ahead of the storm’s arrival.

In the end, the worst case scenario didn’t bear out in Washington D.C. or New York where fears of coastal flooding and damaging winds prompted airports to close and trains to suspend service. The subways were halted in case storm surge pushed rivers over their banks and into the transit systems. Though Irene wasn’t as bad as she could have been, five million people are still without power.

While forecasters accurately predicted the storm’s track and even figured out its timing it missed when it came to determining Irene’s intensity. For as much as scientists know about hurricanes that is the biggest remaining scientific uncertainty. In the last 20 years the ability to track a storm’s path has improved greatly but that doesn’t mean forecasters know ahead of the hurricane making landfall what it will do.

Hurricane Irene was no different. The storm came ashore in the outer banks of North Carolina as predicted as a strong Category 1 storm, giving all indications that it would stay organized and pick up intensity as it returned to sea before making landfall a second time in Virginia and Maryland.

But somewhere in North Carolina it hit a dry patch of air which sucked some of the power from the hurricane, which was then downgraded to a weaker Category 1 as it set its sights on Washington D.C. It tore flags on federal buildings to shreds, downed trees and powerlines but left the U.S. capital relatively unscathed.

Then Irene began to bear down on New York City. A direct hit from a hurricane poses big problems for the 9 million people who live in the low-lying city surrounded by water. Storm surge from a storm like Irene is enough to push rivers over their banks, flooding large sections of lower Manhattan. To make matters worse, Irene was on track to hit New York about high tide.

But the real fear though was high winds. As it churned in the warm Caribbean it grew into a strong Category 3 hurricane. If Irene had roared into Manhattan that strong officials predicted that skyscraper windows would shatter and litter the streets with glass. Fortunately, the wind wasn’t the problem in New York but water was, even though it wasn’t even as wet as it could have been.

The Battery Park and East Village neighborhoods of Manhattan saw significant flooding as did parts of Brooklyn and Queens. So Mayor Michael Bloomberg’s decision to evacuate 300,000 New Yorkers from coastal areas appears to have been the right one.

Across the swollen river, New Jersey also experienced significant flooding. Some towns there may not get power for at least a week.

After Irene left the New York area as a tropical storm, the east coast seemed to let out a collective sigh of relief. And then reports of people stranded upstate began to filter in as Irene made her way through New England.

By far Vermont fared the worst, getting the lion’s share of the flooding. Partly because of a wet summer, the ground was already saturated, leaving the inches of rain that Irene dropped with nowhere to go. It pooled and poured into brooks and streams, turning them into raging rivers.

Here are some of the rain totals.
Bunyan, North Carolina–15.66 inches
New Bern, Williamston, Washington and Greenville, North Carolina–12+ inches
Suffolk and Newland, Virginia–11 inches.
Maryland cities of Plum Point–12.96 inches, Easton–11.34 inches and Hickman–10.5 inches
Tuxedo Park, New York–12 inches
Ellendale and Adamsville, Delaware–10+ inches each
Stockton and Wayne, New Jersey–10+ inches
Berlin, Vermont–10 inches
Savoy, Massachusetts–9+ inches
Lakewood, New Jersey–8.27 inches
Burlington and East Hartford, Connecticut–8+ inches
Philadelphia–6 inches (on top of 13 inches for the month of August where 3 inches is average)

Even before Irene dropped any rain on the mid-Atlantic states, August had already been a record-setting soggy month.

Here are the rainfall totals for the month following the storm, according to AccuWeather.com. New York City (18.95 inches), Newark (18.79 inches), Trenton (14.85 inches) and Philadelphia (19.31 inches), all have set new records for the wettest month on record, thanks in part to Irene.

Some hurricane dynamics

Hurricanes start as tropical depressions, generally blown off the northwest coast of Africa as a tropical wave of low pressure. When a line of squalls along the West African Disturbance Line move offshore the ocean begins to pick up moisture. Meteorologists get a glimpse of what’s coming down the pipeline weeks in advance of a hurricane forming.

Currently, tropical weather forecasters are watching Tropical Depression 12 spin away from Africa toward the Caribbean. By later this week, the depression could work it’s way into Hurricane Katia.

Once a tropical depression forms the coriolis effect helps it begin to rotate. Think of it like the spinning of a buzz saw blade. The storm begins to turn as it sucks up moisture from the warm ocean surface. When it pulls in that moisture it pulls down cooler air from above which gets trapped under the warm, wet and rising air. that continuous feedback loop makes the storm rotate and strengthen.

To turn into a hurricane a tropical depression needs energy. The way it derives that is also from the ocean surface. The warmer the water, the more energy is created, which leads to bigger storms. That is why the hurricane season stretches from June to December. Those are months when the ocean is warmest.

For the most part, hurricanes need ocean surface temperatures of at least 80 degrees to grow. When water temperatures are below 80 degrees hurricanes tend to lose energy and intensity.

Kevin Trenberth is a senior scientists at the National Center for Atmospheric Research. He told Grist, “Owing to higher SSTs [sea surface temperatures] from human activities, the increased water vapor in the atmosphere leads to 5 to 10 percent more rainfall and increases the risk of flooding. He says that water vapor in addition to ocean surface temperature makes hurricanes more ferocious. He adds, “However, because water vapor and higher ocean temperatures help fuel the storm, it is likely to be more intense and bigger as well.”

Meteorologist Jeff Masters says the range of the warm sea surface temperatures have a wider range this August, which gave Irene more power. Before she made landfall in the U.S. Masters said, “This year sea surface temperatures one to three degrees warmer than average extend along the East Coast from North Carolina to New York. Waters of at least 78 degrees F extend all the way to southern New Jersey, which will make it easier for Irene to maintain its strength much farther to the north than a hurricane usually can.”

As the storm hit land and cooler waters Irene lost her punch. By the time she hit New England the wind and rain had effectively separated into two storms. The rain submerged much of Vermont while powerful winds raked north, exploding windows in Montreal office buildings, 300 miles north of New York where that was part of the forecast worst case scenario.

Once the tropical characteristics were gone, Irene became a fast-moving mid-latitude storm racing its way toward the Canadian maritime provinces and out to sea where cold northern waters will suck any remaining strength from her.

But she’ll be remembered as a wet and wild dry run for a major hurricane making landfall on the eastern seaboard and will likely inspire a disaster movie or two.

Is Hurricane Irene a Product of Global Warming?

While emergency managers are feeling lucky to have avoided the worst, they are still concerned that more storms like Irene could rear their damaging heads in densely populated areas. And everyone is remembering that this hurricane came one day shy of the sixth anniversary of Hurricane Katrina, which devastated New Orleans.

As scientists watch sea levels rise, storm surge from hurricanes becomes the biggest threat. The sea has risen 13 inches around New York, turning moderate storm surges associated with tropical storms into major flooding events.

MIT Atmospheric science professor Kerry Emanuel thinks that we are beginning to see a climate signal form in the Atlantic, meaning that after decades of prediction, evidence is emerging that climate is changing and the effects are starting to be felt. Extreme weather seems to be on the rise, including massive hail storms, tornado outbreaks and strong hurricanes.

He says, “One begins to wonder, if you add all those up, maybe you are seeing a global warming effect.”

But science writer Michael Lemonick says asking if Hurricane Irene is a direct result of climate change is actually the wrong question.

He believes we should be asking is climate change making Hurricane Irene worse than it would have been otherwise? To that he says a definitive, Yes.

He says, “For one thing, sea-surface temperatures in the Atlantic Ocean are higher now than they used to be, thanks to global warming, and ocean heat is what gives hurricanes their power. All other things being equal, a warmer ocean means a more powerful storm. It’s hard to say that all other things are exactly equal here, but it’s certainly plausible that Irene would have been a little weaker if precisely the same storm had come through, say, 50 years ago.”

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