Circulation features associated with the record-breaking typhoon landfall on Japan in 2004

Ten typhoons struck Japan in 2004, which was an all-time high although the total number of typhoons formed over the western North Pacific was slightly above normal. The characteristics of typhoon activity are the unusually high number of typhoons approaching Japan in the early summer (June) and fall (September and October) and the frequent landfalls in the middle summer (July and August). Seasonal mean large-scale circulation in 2004 was characterized by a split of the North Pacific subtropical high (NPSH) east of Taiwan and persistent anticyclonic anomalies to the southeast of Japan, enabling typhoons to penetrate the weakened NPSH and move to Japan. Two possible causes are suggested here to maintain the persistent anticyclonic anomalies near Japan: one is positive feedback between typhoons moving northward and midlatitude circulation near Japan, the other is response to the broad-scale tropical deep convection. A further modeling study is required to substantiate these arguments.