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Mysterious Weather Pulses Help Predict Hurricanes
Aug. 31, 2009 -- Every month or so, a wave of mysterious weather pops up over the Indian Ocean and begins marching eastward through the tropics.
Scientists are unsure what causes it, but a new study has shown that tracking these pulses -- known as the Madden Julian Oscillation -- could allow weather forecasters to predict hurricane and tropical storm formation up to three weeks ahead of time.
Forecasters know enough about the conditions that produce these vicious storms to make annual guesses about how active each hurricane season might be, and to forecast their behavior about five days into the future once they form.
But in between is a vast chasm of uncertainty.
Frederic Vitart of the European Center for Medium-Range Weather Forecasts in the United Kingdom is beginning to bridge that gap, by shedding light on the way the Oscillation influences tropical storm formation, intensity and movement.
Alternating between a vast province of moist, stormy air or an unusually dry patch, the Oscillation slowly blows through the tropics, often circling the globe several times. In a computer simulation of the last 20 years of hurricane seasons, Vitart showed it could increase or decrease risk that a storm would make landfall by as much as 50 percent.
The results were published earlier this month in the journal Geophysical Research Letters.
"The Madden Julian Oscillation creates large-scale conditions which are known to favor tropical storm genesis," he said, bringing with it increased moisture and weakening wind shear.
Vitart's model reliably predicts storm formation out to about 20 days. But the Oscillation is a diffuse, widespread weather pattern; using it to forecast hurricanes can dramatically improve forecasts, but it does not turn weather models into crystal balls.
Even armed with knowledge of the Oscillation's influence on Hurricane Katrina, for instance, no one could have foreseen the storm's devastating strike on New Orleans.
"We may not be able to predict the strike of a storm at a given time and given location, but we can predict if the probability of a tropical storm strike will increase or decrease in the next few weeks over a large area," Vitart said.
"I think that the forecasting that would arise from the Madden Julian Oscillation would be different in nature from the three- and five-day operational track forecasts that currently come out of the National Hurricane Center, which predict the track (and cone of uncertainty) of a storm that already exists," Gabriel Vecchi of the National Oceanic and Atmospheric Administration in Princeton, New Jersey said in an email to Discovery News.
"The Madden Julian Oscillation would help us to predict the genesis of a storm that doesn't exist yet, and the likely character of its track, landfall, etc."
Vitart added that he is working on developing a way to use this type of forecasting to construct maps that display advanced warning of increased risk of hurricane strikes for a given stretch of islands or coastline.
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