Using two kinds of the monthly mean reanalyzed data of the ECMWF (1958-2001) and NCEP/NCAR

the relationship between onset dates of the South China Sea (SCS) summer monsoon and the preceding meteorological fields is analyzed. It is found that there is a marked correlation between the onset dates and the wind fields (u

v

ω)

geopotential height fields

air temperature fields in February. The forecast zones are defined as high correlation coefficient zones. Ten forecast factors are selected from the forecast zones. The results indicate that the onset dates are closely related to the factors that can forecast and diagnose SCS summer monsoon onset. Using these forecast factors and SAS statistic analysis system

the regressionforecast equation is established to forecast the monsoon onset date. The correlation coefficients between the fitting onset dates of SCS summer monsoon based on regressionforecast equation and onset dates from different references are over the 95% significance level. The regressionforecast equation can forecast monsoon onset dates with low error. This method is a new way to forecast SCS summer monsoon onset dates.