Heatwave in Japan

  • Figure 1. Map of surface pressure at 0000UTC 12/07/2013. High pressure over the Pacific can be seen to extend west over Japan. Also note the presence of Typhoon Soulik approaching Taiwan.

    Figure 2. Maximum temperature observations across Japan on Thursday. Temperatures in white represent 35C and higher.

  • Heatwave in Japan
    13.07.2013 14:45

    Whilst many areas of the UK have been experiencing above average temperatures for more than a week now, parts of Japan have had to endure severe and oppressive heat that has left at least 12 people dead and thousands others requiring hospital treatment.

    Although July is typically hot and humid in Japan and marks the end of the rainy season, the searing and prolonged heatwave has brought back memories of 2010 when scores were killed by the heat. The responsible meteorological factor has been a large area of high pressure extending westwards over the Pacific Ocean and across the Japanese archipelago (Figure 1). In high pressure, air sinks from the higher parts of the atmosphere towards the surface and when this is combined with intense daytime solar heating, the effect is for hot air to be trapped in the lower parts of the atmosphere. Moreover, areas of high pressure can often be stubborn to shift, hence why heatwaves can sometimes persist for considerable periods.

    Numerous weather stations have recorded temperatures higher than 35C (95F) since the start of July and the Japanese Meteorological Agency reported that 39C (102F) was exceeded for the first time this summer on Tuesday in Koshu (approximately 80km west of Tokyo). The map of temperature observations for Thursday (Figure 2) illustrates the wide spatial distribution of the heat, especially across central and south-western prefectures. Given that average maximum temperatures for July range from 25C in Sapporo to 32C in Kagoshima, recorded temperatures have been well above the seasonal average.

    There has been a slight reprieve, however, over the past 24 hours as somewhat less warm air has begun to drift in from the north and the high pressure has started to decline. This should ensure temperatures return to near-normal for Sunday and the start of next week, hopefully reducing the number of people suffering from heat exhaustion and heatstroke symptoms.


    By: Nick Prebble