All About Tropical WavesAdded : Monday at 14:10 A bit of a digress today away from the UK weather and a little about tropical waves. Now, whilst you may think tropical waves are those things which lap up on the beach in the Maldives whilst you are sipping your cocktail, tropical waves are in fact regions of cloud and instability which move off the West coast of Africa :-
If you take a look at the image above, then you can see Hurricane Sam in the Atlantic, another wave in between South America and Africa and yet another wave coming off the coast of Africa.
Tropical waves are caused by fluctuations in the Easterly African Jet. When the jet fluctuates or meanders, so the air either speeds up or slows down. When this happens, a bit like motorway traffic, you end up with congestion in areas. This "congestion" forces the air to rise and you end up with a region of cloudiness and thunderstorms drifting West.
Normally, these dissipate in the open ocean, but if there is a combination of warm seas, lack of low and mid level wind (shear) and the waves are around 10 degrees North of the Equator, then the thunderstorms continue and interact with each other and start to spin.
At this time of the year, the band of thunderstorms called the ITCZ are actually sitting around 10 degrees North, which is why tropical systems are always more common in September/October.
Once the ITCZ drifts South towards the equator, so the Coriolis Effect becomes less and any tropical waves continue to remain just that, a wave.
Here was yesterdays Atlantic satellite image and you can clearly see the waves coming off the African Coast :-
Sometimes, when tropical features form further North, around 25 degrees North, they encounter more in the way of shear and this results in a more active system if it manages to form. These systems are called Screaming Eagle Waves because they look like an eagle screaming and looking down on its prey... apparently, see what you think :-
Of course, not every wave which comes off Africa turns into a raging hurricane. Things like shear, African dust, cool sea temperatures and not enough Coriolis force are all factors which can limit or stifle any development, but with over half of all Atlantic tropical systems developing from Tropical Waves off Africa, so it's rather important that we always keep an eye on them through the Atlantic Hurricane Season.
Couldn't see a Screaming Eagle? No, we couldn't either...
METEOROLOGIST : MARSH |