An experiential index for prediction of regional rainstorm in Guangxi has been found, by analyzing EC wind data and defining the south and north wind indices of low latitudes. The wind indices in the cases that regional rainstorms occur or not are collected based on 1115 front cases during 1970-2009. The distribution of probability of regional rainstorm versus the wind indices is calculated, while the wind indices are combined with experiential corrections. As a result of examining 440 front rainstorm cases from 1970 to 2009, the proportion of the experiential index corresponding to the time of rainstorm happening is 74.5%, the corresponding to the position of rainstorm is 75.9%, and the corresponding to the intensity of rainstorm is 67%. These facts manifest that the experiential index is reasonable and available in actual predictions.