Risk of Heat Wave in Japan Higher Than Usual July-Sept.; Meteorological Agency Calls for Preventative Measures for Heatstroke

Yomiuri Shimbun file photo
People cool off with mist on a sweltering day above 30 C in Minato Ward, Tokyo, in May 2023.

A higher-than-usual risk of a heat wave is expected from July to September as the North Pacific High — a high-pressure system over the Pacific Ocean — intensifies, according to the Japan Meteorological Agency’s three-month weather forecast released on Tuesday.

The agency is calling for measures to prevent heatstroke.

The probability of average temperatures exceeding those of the average year is 50% in northern Japan, 60% in eastern and western Japan, and 70% in Okinawa and Amami. Forecasted precipitation is about the same or higher than the average year in western Japan and about the same level in northern and eastern Japan.

A La Nina phenomenon, in which sea surface temperatures near the equator become cooler than normal, is expected to occur off the coast of Peru, South America, from summer to autumn. As a result, the northwestward extension of the North Pacific High and the northeastward extension of the Tibetan High from the Chinese mainland will strengthen, bringing a possibility that the two will overlap over Japan. Air temperatures tend to increase when a high-pressure system extends to high altitudes.