Shulman Advisory

Turning Up the Heat: Japan’s Sweltering June 2025

Publication date: June 30, 2025 Turning Up the Heat: Japan’s Sweltering June 2025

Turning Up the Heat: Japan’s Sweltering June 2025

This article was co-produced by Shulman Advisory and Atmospheric G2. Drawing on our combined expertise in power markets and weather analysis, we assess Japan’s June 2025 temperatures, their immediate impact on power markets and an outlook for the coming weeks.

The weather in Japan has been notably hotter and drier than normal over the past week.  Specifically, from the 15th to the 19th of June, the observed daily high temperatures ranged from 29°C to 32°C, consistently exceeding the 30-year normal average of around 25°C–26°C for that time of year. Such persistent above-average temperatures are often associated with reduced precipitation and drier conditions, compounding the effects of the heat and increasing the likelihood of drought and associated environmental impacts.

The record-breaking temperatures triggered a notable reaction in Japan’s electricity markets, with peak JEPX daily system spot prices increasing by JPY 3.3 to 9.86 / kWh between 16 – 19 June. The JEPX spot price surged to JPY 30.56 / kWh between 6pm and 7.30pm on 19 June, representing a 38% increase from the same date last year. These price spikes reflected the intense strain on the power system as cooling demand soared across the nation. The impact on demand was less pronounced, with demand tracking generally in line with this time last year. However, if these high temperature trends continue, then we may expect to see demand continue to increase, along with power prices.

The 15-day weather forecast across Japan’s power zones (PZs) indicates a sustained period of hotter-than-normal conditions, with maximum temperatures consistently exceeding 30°C in most regions. From Hokkaido to Chugoku, nearly all zones display shades of orange and red, signaling significant deviations above the 30-year seasonal norms. Notably, Chubu_PZ, Hokuriku_PZ, and Kansai_PZ are expected to experience particularly intense heat, with high temperatures reaching up to 34°C—well above the historical averages in the 27°C–28°C range. Even the typically cooler Tohoku_PZ and Hokkaido_PZ show several days of anomalously high temperatures, especially toward the end of June and early July. 

The consistent forecast highs across all regions, coupled with relatively warm lows (around 23°C–26°C), suggest minimal nighttime cooling, which could stress power demand due to increased cooling needs. Overall, the outlook underscores a persistent and widespread heatwave pattern gripping Japan, intensifying the demand on energy infrastructure and raising potential concerns for public health and resource management.

Figure 1. The minimum and maximum temperature outlook compared against the 30-year average; pale orange represents +1.5°C to +3°C, dark orange represents +3°C to 4.5°C and red represents +4.5°C to +8°C (provided by Atmospheric G2).
Figure 1. The minimum and maximum temperature outlook compared against the 30-year average; pale orange represents +1.5°C to +3°C, dark orange represents +3°C to 4.5°C and red represents +4.5°C to +8°C (provided by Atmospheric G2).

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This is the sixth article in our mini-series on harnessing weather intelligence to optimize renewable asset performance. If you missed the previous articles, you can catch up here:

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