The relationship between the unusual summer weather over Japan and the tropical conditions in 1988 was investigated. It was shown that the cool and rainy summer over Japan can be directly explained by the weak convective activity in the tropical western Pacific around the Philippines. The subtropical high in the western Pacific did not fully develop due to the inactive tropical convection and the low-pressure zones prevailed around Japan for July and August.
Analyses of wind and Outgoing Longwave Radiation (OLR) data show that the convection center corresponding to the rising center of the tropical east-west circulation (Walker circulation) was abnormally shifted westward from the normal position over the tropical western Pacific towards the Bay of Bengal. This westward shift of the convection center may result in the lack of convective activity in the tropical western Pacific probably due to the compensating downward motion.
The tropical regions during the 1988 summer were characterized by the strongest La Nina condition since 1975 and above-normal SST over the Indian Ocean. It is speculated that the warmer SST over the Indian Ocean together with the extreme La Nina condition might force the convection center to move westward toward the Bay of Bengal.