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Hurricanes and the Deadly Ripple

August 22, 2011

The MJO helped Irene grow into a dangerous hurricane. Hurricane Irene hitting Puerto Rico. Source: NOAA

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It didn’t seem deadly in the early days. Back in the 1970s—the era of shaggy hair and bad shirts—two scientists, Roland Madden and Paul Julian, explored an obscure wind pattern around Singapore.

The two men discovered a 30 ̶ 60-day cycle of wind patterns and named it the Madden Julian Oscillation (MJO).

It took 30 years for scientist to learn that this pattern makes tropical storms into deadly hurricanes!

Here is how it works. The MJO is a weakening and strengthening of tropical trade winds. When the wind is weak, the ocean surface is quiet and the sun warms it. When it was strong, it ruffles and cools the surface. Basically the weak winds linger for a few weeks, allowing the water to warm. Then the area of weak winds drifts east, followed by an area of strong winds. The waters cool.

To a satellite, it looks like large areas of warm water, called Kelvin waves, slowly moving east, followed by areas of cool water. Over each drifting pool of water are layers of winds that shape weather. Over the cooler waters, winds are very favorable for rainfall, tropical storms and hurricanes.

The MJO and Kelvin waves start on the east coast of Africa, then drift east across the Indian and Pacific Oceans. As they drift, they alter giant monsoons and typhoons. They even create the Pineapple Express storms that bring flooding rains to Washington and Oregon.

Expand below image (PDF).

SOURCE: © The Browning Newsletter

Then in the past decade, scientists discovered that the MJO winds drift into the Atlantic. When the stronger wind pattern enters the Atlantic, it causes the hurricane season to explode.

That is what is happening now. The Atlantic reaches its warmest temperatures in late August and early September. Just when it reached its peak, the MJO drifted over it and created perfect conditions for tropical storms and hurricanes! Yikes! In less than 10 days, three tropical storms (Franklin, Gert and Harvey) and Hurricane Irene have developed. Irene shows signs of hitting the US.

It was only an obscure ripple when two weather dudes discovered the MJO in the Seventies. But if you watch it coming, you can determine when the killer hurricanes will develop. Just remember —this ripple packs a punch!

See hurricane forecasts for the 2011 season here.

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Evelyn Browning Garriss, historical climatologist, is a longtime writer for The Old Farmer's Almanac. She is also editor of The Browning World Climate Bulletin and has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.

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Another Piece to the Weather/Climate Puzzle

By jeltez42

Very interesting article. I wonder how many more obscure things are out there contributing to our weather that need to be "discovered".

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