Tropical Cyclones need two main ingredients in order for it to form. These ingredients are: a cluster of thunderstorms and a warm body of water that is at least 27º C.
When the warm, tropical ocean is under a developing storm the water evaporates and then condenses to form clouds and heat is released throughout the process.
The heat energy and the rotation of the Earth combined together gets the cyclone spinning and propels it forward.
The wall of the eye is the deadliest part of a cyclone. Here the strongest winds and greatest rainfall are found. The eye is usually 40 km in diameter, but can range in size from less than 10 km to over 100 km depending on the size of the cyclone itself.
Tropical cyclones form between approximately 5° and 30° latitude and initially move westward (owing to easterly winds) and slightly towards the poles
The cross-section of cyclone:
Climatic Conditions leading to the occurrence of Tropical Cyclones
In order for tropical cyclones to form there has to be climatic factors because cyclones don't form spontaneously. Tropical cyclones may occasionally form without these factors but, however these are the most important.
The most important and most common factor is that the water temperature has to be between 26-27º C all the way down to a depth of 50m (160ft). When the water is at this temperature, the atmosphere becomes unstable enough to sustain convection and thunderstorms.
Another important factor is rapid cooling with height. This allows the heat energy (warm air) to be released and this is what powers the cyclone. High humidity is needed, especially in the lower-to-mid troposphere; when there is a great amount of moisture in the atmosphere, conditions are favourable for disturbances to develop. Tropical cyclones generally need to form 555km or 5º of latitude away from the Equator in order for the Coriolis effect to deflect winds blowing towards the low pressure centre and create circulation. The final factor is that a cyclone needs a pre-existing system of disturbed weather in order to form.