What causes typhoons to change speed and direction?

Answer 1

Typhoons and other tropical cyclones are steered by large scale wind patterns, which are mostly determined by high and low pressure systems. High pressure systems, which circulate clockwise in the northern hemisphere tend to cause typhoons to make right turns while low pressure systems, which have counterclockwise winds cause them to make left turns. (This is reversed in the southern hemisphere, but storms there are not called typhoons). There is a semipermanent subtropical ridge of high pressure which causes many typhoons to start out moving west and then to turn north and east. The strength of these winds are what determines the speed of these winds. In the absence of such steering winds typhoons will move slowly and can even become stationary. Slow moving storms such as this tend to have erratic paths.

Since a typhoon is a low pressure system in the northern hemisphere its winds will always rotate counterclockwise.The speed of the winds are determined by a number of factors that influence intensity. A typhoon will tend to strengthen when it is over warm water in a mass of moist air and there is little to no wind shear (i.e. there is little difference between the speed and direction of upper and lower level winds). A typhoon will weaken and possibly dissipate if it moves over land or cold water or if it encounters dry air or strong wind shear.