Tropical revolving storm (TRS) is a warm-core, low-pressure system, around which the air circulation is anti-clockwise, in the Northern Hemisphere (NH) and clockwise, in the Southern Hemisphere (SH).
It consists of a rotating mass of warm and humid air and creates thunderstorms with strong winds, flooding rain, high waves, damaging storm surge etc.
It devolves over large bodies of warm water and normally dies, when moves over land. For this reason, coastal regions receive significant damages from a tropical cyclone; where as inland regions are relatively safe from this.
The diameter of a tropical storm is normally less than 500 nm even can be only 100 nm at its early stage of development.
TRS is common in various places of the world, but they can be called as below local trams,
- “Cyclones” is used in the Bay of Bengal and Arabian Sea.
- “Hurricane” is used in the western side of north Atlantic and south Pacific.
- “Cordonazo” is used in the eastern side of North Pacific.
- “Typhoon” is used in the western side of North Pacific.
- “Willy – willy” is used in the eastern side of South Indian Ocean.
Basic requirements to form tropical storms:
There are six main requirements to develop tropical revolving storms. These are the basic requirements, but do not give any guarantee of forming such cyclones.
- Sufficiently warm temperatures : Normally an ocean temperature of 26.5°C is the minimum requirement for TRS formation. Warm ocean water must exist over a sufficient depth of at least 50 meter. These warm waters are necessary to fuel the heat engine of the tropical cyclone.
- Potentially unstable atmosphere : There must be an atmosphere that cools quickly with height, so that it becomes potentially unstable. If the air is unstable, then it will continue rising and the disturbance will grow. This is required to maintain convection for an extended period of time.
- High relative humidity : A necessary amount of relative humidity must be present in the lower to middle levels of the troposphere. The required amount of humidity is about 50 to 60%.
- Adequate value of Coriolis Effect : It has been observed that TRS does not form within 3 degrees latitude from the equator, as Coriolis effect is negligible at the equator. So a minimum distance of 500 km from the equator is normally needed to from TRS.
- Largest low pressure : Pressure must be lowered with largest amount and this LP area must be surrounded by areas of HP, which is required for preexisting near-surface disturbance.
- Limited vertical wind shear : Limited vertical wind shear can be positive for tropical cyclone formation. This amount should be less than 10 m/s between the surface and the tropopause. On other hand, strong wind shear can blow the tropical cyclone apart.