NBC2 Animation: How the West African Monsoon can spawn tropical systems

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Take note! We are rapidly approaching the time of year when it’s important to check what the weather is doing in western Africa.

That’s because August and September mark the typical peak of the West African Monsoon, a weather feature you could think of as a tropical wave factory.

And though hurricanes don’t spin up from every tropical wave that develops over Africa, historically what happens here has marked the starting line for long-haul tropical systems that have had direct impacts here.

Monsoons are seasonal wind reversals that impact several locations on Earth.

One of those places would be western Africa, where in late summer hot and dry winds from northern deserts collide with humid winds from the west-southwest over the Atlantic.

This collision of air forces it to rise, cool, condense and cluster into waves of monsoon rains.

Over this part of Africa, the prevailing winds move from east to west. This means tropical waves chug along westward and eventually reach the Atlantic Ocean.

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That’s where some waves get stronger and others fall apart. The ones that get stronger typically find themselves in an environment with warm ocean water, minimal wind shear and no dry air.

Waves that struggle typically move over less-than-optimal water conditions, regions of the atmosphere with stronger wind aloft and wedges of dry air like from the Saharan Air Layer that can derail their development.

The waves that survive typically find that over the warm waters of the Atlantic the showers and thunderstorms have what they need to continue growing vertically. As air rises, it cools and condenses helping to increase the coverage of rain and storms. This process releases latent heat energy which hurricanes use for fuel.

As they form if enough air rises, the storms begin to form an area of relatively lower pressure in the atmosphere. Because of the spin of the Earth, areas of lower pressure spin counter-clockwise, which starts to swirl the thunderstorms around the region of lowest pressure.

Pending no hurdles (like wind shear or dry air for example) these tropical systems can become weather monsters. Long-haul systems that have travelled thousands of miles include notable storms like Irma in 2017, Florence in 2018, Hugo in 1989 and Ivan in 2004.

Watch the attached video from NBC2 News at 3 for an NBC2 Animation walking you through the process of the West African Monsoon.

Tags: Weather blog

 

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