Typhoons increased, got slower over 40 years: Japan meteorological institute

TOKYO — The number of typhoons approaching Japan from the Pacific Ocean has surged in the last 40 years, with an average of 1.2 more typhoons per season reaching Tokyo in 2019 compared to 1980.
The Japan Meteorological Agency’s Meteorological Research Institute announced their findings on Aug. 25. They reported that it showed approaching typhoons have become stronger and slower moving.
According to the institute, an average of 25.6 typhoons were formed yearly between 1981 and 2010. Of these, the eyes of an average of 11.4 typhoons came within 300 kilometers of meteorological observatories and elsewhere in Japan each year.
The institute statistically processed the observed data from 1980 to 2019, and found that an average of 2.35 typhoons approached Tokyo in typhoon seasons during the second half of the 40-year period — about 1.5 times the average in the first half. The institute then reanalyzed the figure by rate of increase, and found that the number of typhoons in a season had increased by about 1.2 over 40 years.
When limited to powerful typhoons with a central pressure of less than 980 hectopascals, the average number of typhoons that approached Tokyo in the second half of the observed time was 2.5 times the average of the first half. Typhoons with almost the same intensity also moved 36% slower in the second 20 years than in the first. This is said to be the reason why Japan has experienced powerful storms and other phenomena brought by typhoons for longer periods.
In line with Tokyo’s experience, a tendency toward an increase in typhoons was observed in other areas facing the Pacific Ocean. Though the path of a typhoon is greatly affected by where the Pacific high subtropical anticyclone is located, its pressure system has enlarged about 500 kilometers west and 300 kilometers north over the 20 years until 2019, pushing typhoons into tracking even nearer to the Pacific Ocean coast.
It is believed that because prevailing winds headed west, known as westerlies, have moved north, west-moving wind speeds have weakened over areas on the coast of the Pacific Ocean, making typhoons move more slowly in recent years.
(Japanese original by Tomoko Mimata, Science & Environment News Department)