Certain ingredients are needed for a tropical storm to develop:
Warm oceans with temperatures of over 27 °C
Winds near the ocean surface blowing from different directions converging (meeting) and causing air to rise and storm clouds to form
Winds which do not vary greatly with height - known as low wind shear. This allows the storm clouds to rise vertically to high levels
Sufficient distance from the equator to provide spin or twist (at the equator there is not enough spin from the rotation of the earth – the Coriolis effect)
Stages of Tropical Storm Formation
Air rises, drawing water vapour from the warm ocean surface.
Evaporated air cools as it rises and condenses to form towering thunderstrom clouds.
As the air condenses it releases heat which powers the storm and draws up more and more water from the ocean.
Several smaller thunderstorms join together to form one giant thunderstorm. When surface winds reach an average of 75 miles per hour the storm becomes classed as a tropical storm.
The storm develops an eye at its centre, where conditions are calm. Air descends rapidly within the eye. The outer edge of the eye is known as the eye wall. The most intense weather conditions are felt at the eye wall (heavy rain and very strong winds).
As the tropical storm is moved across the ocean by the prevailing wind, it continues to gather strength.
On reaching land, the storm's energy supply is cut off. Friction with the land slows it down and it begins to weaken.
Tropical storm - Structure
Three main features make up a tropical storm:
Eye – the centre of a tropical storm where sinking air causes relatively calm, clear conditions.
Eye wall – the towering banks of cloud bearing heavy rainfall which surround the eye. Here there are winds in excess of 120km/h.
Rain bands – Rain bands are bands of clouds and thunderstorms that spiral out from the eye wall. Heavy bursts of rain and wind are usually associated with rain bands. These structures form the outer most fringes of the tropical storm structure, and the winds contained within the bands decrease outward from the eye wall.