By analyzing the relative data and comparing with similar historic cases

the characteristics and causes of typhoon Sally are analysed here. The conclusions are: Sally is characterized by stable track

quick movement

quick offshore development and strong landing intensity

etc. The strong and stable west Pacific high pressure and the warm zones in the middle troposphere are the major causes of the stable track and quick movement of the typhoon. The strong and stable subtropical high pressure

the high relative humidity in the middle troposphere

the water vapor convergence in the lower level

and the divergence field in the upper level provide advantages to the offshore development of the cyclone.