Why Hurricane Irene Fizzled Out After Initial Scare
By on August 29th, 2011

When they got it wrong, they got it spectacularly wrong! Meteorologists have become the newest subject of many jokes in recent days, as they got the storm prediction of Irene embarrassingly wrong. Hurricane Irene was nowhere near as big as it was made out to be! What was supposed to be a major storm and cause widespread mayhem, fizzled out to become a bit more than a strong breeze. Yes, it did rain and yes, trees were uprooted in many places, but the weather guys had warned us about far worse things. We would like to stand behind the weather forecasters and explain why the predictions were so far off-the-mark.

Flooding in New York City

Irene’s Energy Sink

The greatest sink of Irene’s energy was the cold water it was moving into. As storms move northwards, the ocean temperature drops and the energy reduces. This effect is marked if there are no other sources of energy like warm water currents. The cold waters east of Delaware and Maryland did the trick. Further, any storm weakens as it encounters terrain, as it cannot pick up energy as it could from over the water surface. What was really surprising in Irene’s case was the rapidity with which the storm downgraded itself from a fearsome Category 3 storm with wind speed of 115 mph to a Tropical Storm barely registering 60 mph.

The Collapse that saved many others

The US Meteorological Department provides the answer. There was a wall of moisture laden clouds spinning at over 100 mph near the eye of the Hurricane. This inner eyewall’ was supposed to collapse and be replaced by an outer eyewall’, which would then shrink and replace the inner eyewall. While the collapse of the inner eyewall would represent a decrease in storm intensity, the replacement procedure has been associated with the strengthening of the storm. In case of Irene, the outer eyewall never materialized and when the inner eyewall fell, the storm weakened rapidly. The energy, which was supposed to be concentrated over a small area, spread out. The rain bands disassembled themselves and the result was a Tropical Storm.

Another factor was the wind system over the Great Lake region, which spread eastwards and sapped away energy from the Hurricane, through a process called wind-shear’.

Be Fair!

To be fair to meteorologists, this kind of process involves so many parameters that it is impossible to be spot-on every time. Being on high alert and then relaxing is better than being caught off-guard.

An uprooted tree in New York City: Not Enough Huh?

Irene was not completely harmless. It did kill 16 people, uprooted several trees and flooded Lower Manhattan and New York. It is indeed fortunate that nothing worse happened.

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Author: Debjyoti Bardhan Google Profile for Debjyoti Bardhan
Is a science geek, currently pursuing some sort of a degree (called a PhD) in Physics at TIFR, Mumbai. An enthusiastic but useless amateur photographer, his most favourite activity is simply lazing around. He is interested in all things interesting and scientific.

Debjyoti Bardhan has written and can be contacted at debjyoti@techie-buzz.com.
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