Sierra Leone falls victim to highly active West African storm pattern but why?

Written by on August 19, 2017 in Africa, Rest of World, Summer 2017 with 0 Comments

We often overlook the effects of African easterly waves on African nations and only focus on them particularly once out over the open Atlantic.

What are African easterly waves and the easterly jet they ride along?

Commencing their journey over the Ethiopian Highlands, tropical waves are ‘waves of energy within the atmosphere where there’s enhanced lift or upward motion sustaining thunderstorms activity. They gain energy as they progress west over the deep jungles of equatorial Africa, riding the African easterly jet or AEJ is a convergence wind which forms within a thermal boundary sepearting hot, dry Saharan air from the cooler, humid equatorial air just like the jet stream circling the mid latitudes.

However to better understand the whys, you must look at the global circulation and cells.

As you can see from the graphic above, there are two high pressure cells, one north and the other south of the equator, these are known as the Hadley cells. Large scale sinking air is hot and dry hence why the great deserts of the world sit beneath them. The winds circling these two cells of subsidence merge within the intertropical convergence zone or ITCZ.

It’s within this convergence zone that the air is forced to rise generating thunderstorms which naturally cool down the equatorial region. These thunderstorms are nature’s way of balancing out the heat budget of the tropics.

The below infrared image from July shows the blow up of thunderstorms over equatorial Africa’s rain forest which all drift westwards aboard the AEJ or African easterly jet. Keep in mind that the air in the S hem moves towards the equator from the SE and in the N hem from the NE, helped by the Coriolis effect, winds blow westwards in the tropics while eastwards in our mid latitude region.

With tremendous heat and humidity, strong upward motion within the equatorial region generates big thunderstorms and these release tremendous rains. By the time some of these waves reach Senegal, Guinea and Sierra Leone on Africa’s west-central Atlantic coast, they’re mature and can be immense thunderstorm complexes.

This years African wave train got off to a very early and strong start with strong waves more typical of mid August.

Sierra Leone situated south of Senegal and Guinea is in the midst of it’s rainy season and has received twice the normal rainfall for the last 90-days thanks to the highly active African wave train.

The result of the tremendous rainfall over Sierra Leone has been truly devastating.

The reason for such a fast and furious start to the rainy season may be partially down to the intense heat over the Sahara early on.

FEATURED IMAGE CREDIT: Nazareth House Apostolate Blog

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