The formation of a tropical cyclone begins when Sun heats the ocean, which heats air above it, causing that air to be warm and wet. The warm air rises and cools, causing the water vapor in it to condense into clouds. Condensation releases heat into the air, which warms more air, which rises and condenses to build the clouds higher and higher into columns. The Coriolis Effect causes the moving air to curve, which causes the cloud columns to slowly begin to rotate.
By now the weather system is a tropical disturbance. Clouds at the top of the columns cool, causing more water vapor to condense, which releases heat, which makes the clouds at the top warm up again. Warm temperatures mean the air molecules are moving faster, which results in an increase in pressure. Think of it this way: if you had a container full of air and then warmed the air up, the air molecules would move faster, causing them to hit the sides of the container harder. The strain on the sides of the container is a result of the increased pressure inside the container.
Now the cloud tops are a high pressure area. Air moves from regions of higher pressure to lower pressure, so wind moves outward from the columns of clouds to regions of lower pressure. Basically, the top of the cloud columns are unstable, causing them to topple over, causing the storm to spread out. The wind moves faster and faster, causing the weather system to now be known as a tropical depression.
Air at the ocean's surface continues to rise, cool, condense--which releases heat, which warms the clouds, and builds them up again. This is known as an infinite feedback loop. The top of the cloud columns continue to spread outward, but eventually fall down into areas of lower pressure. Eventually, a series of regions of rising and sinking air forms, creating distinct bands within the storm. At this point, winds are usually fast enough to categorize the system as a tropical storm. This is when meteorologists typically give the storm a name.
Scientists do not know exactly how the eye of the storm forms. Some theorize that it forms as a result of downward pressure as a result of the radial velocity of the storm. Others theorize that heat released at the storm's center causes the clouds to dry out. Whatever the reason, the formation of an eye means that the storm is strong and relatively organized.
Scientists also don't know what will cause a tropical storm to become a full-blown tropical cyclone. If the proper conditions are maintained and the storm is stable, winds will increase to the point where it will become a hurricane, typhoon, or cyclone. However, because scientists don't know the precise conditions necessary and minor changes in vertical wind shear or temperatures could cause the storm to destabilize, no one is able to predict for certain whether a tropical storm will end up as a tropical cyclone.
