In the Guinea lands of west Africa, a violent storm often known as an Africa tornado. It consists of a squall blowing from a severe thunderstorm often starting very suddenly and lasting only a short time but it may cause considerable destruction land and sea. It is usually accompanied by torrential rain. It is more liable to take place during the day when the surface air is strongly heated and is most frequent during the transition periods between the wet and dry seasons.
The African tornado is caused by the meeting of warm, damp monsoonal air from the south west with dry north easterly air from the Sahara. It has a front several kilometers in length sometimes extending to as much as 300 kilometers.An extremely violent whirlwind covering a relatively small area. Its diameter being usually less than 500 m. It is most frequent in the United States, east of the Rocky mountains, especially on the central plains of the basin where hot, damp air from the gulf of mexico meets cool dry air from the north.
It causes great destruction along its narrow track wind velocities near the center are estimated to exceed 300 km per hour and trees are uprooted, buildings completely destroyed. The tornado is usually accompanied by heavy rain and thunder. It occurs most frequently during spring and early summer almost always in the afternoon, when surface heating reaches a maximum.
In a suitable meteorological situation, when an extensive area of low atmospheric pressure exists several tornadoes may develop on the same day. In the United states it is sometimes known as a twister on account of the twisting motion of the funnel shaped cloud at its top.