The invention provides a determination method and 
system, and a forecast method and 
system for a probability of causing ash 
haze of a coastal region by tropical cyclones. The determination method comprises the steps of collecting 
tropical cyclone path 
point data with influence on the 
visibility of a to-be-tested region, and 
visibility and 
relative humidity data of the to-be-tested region in a corresponding time; performing classification on the 
tropical cyclone path 
point data according to the intensities to obtain various types of 
tropical cyclone path 
point data; and dividing a prediction range of the to-be-tested region into a plurality of intervals, reserving a path point of a same tropical 
cyclone in the intervals for the tropical 
cyclone under each intensity, calculating the probability of causing the ash 
haze of the to-be-tested region by the tropical 
cyclone in the intervals according to the reserved path point data and the 
visibility data of the corresponding to-be-tested region, and performing interpolation operation according to 
longitude and 
latitude of a predetermined position in the intervals and the probability of causing the ash 
haze of the to-be-tested region by the tropical cyclone under each intensity in the intervals, thereby obtaining probability distribution of causing the ash haze of the to-be-tested region by the tropical cyclones under all the intensities. According to the determination method and 
system, and the forecast method and system, a reliable basis can be provided for weather predicting and alarming of influence of the tropical cyclones on the ash haze.