A typical tropical monsoon rainstorm process during l984 ‘Mei-Yu’ peiodover Jiang-Huai River areas was analyzed in this paper. It is found that this process isresuIted from the meridional development of the westerlies in midlatitudes and a ty-phoon which developed over the South China Sea and finally landed over vietnam。Strong eastward moving warm air currents in the east part of the Tibet-trough in mid-latitudes help the low-level jet stream

which is just located in the outer ring of the ty-phoon

rush northward and intensify again.That is called the effect of warm advection。While the tropical monsoons invade into the mainland further and further

through themoist process effect

strong divergence at l00 hPa and relative strong upward motiondevelop rapidly. Consequently

heavy rain occurs.