Japan’s Summer 2026 Weather Forecast and Its Impact on the Energy Sector: Extreme Heat, Renewable Energy Generation, and Typhoon Risks Explained

2026.04.16

In the energy sector in the summer of 2026, the combination of “increased electricity demand due to extreme heat” and “fluctuations in solar power generation” may become a critical turning point for electricity supply-demand balance and market prices.

This summer, as in 2025, there is a possibility of an early end to the rainy season and an early arrival of extreme heat, which may also lead to an earlier peak in cooling demand due to high temperatures. Meanwhile, solar power generation may fluctuate depending on sunshine conditions and rainfall patterns, and in the latter half of summer, the approach of typhoons may increase operational risks for wind power generation and power facilities.

The key points for the energy sector in the summer of 2026 are as follows:

• Increase in electricity demand due to a high-temperature trend (especially peak demand and nighttime demand)
• Fluctuations in solar power generation due to sunshine and rainfall
• Suspension of wind power generation and impacts on facilities due to typhoons

This article outlines the main points relevant to the energy sector, including changes in electricity demand caused by extreme heat and impacts on solar and wind power generation, based on the weather outlook for the summer of 2026.

For details of the summer 2026 weather forecast, please see: Summer 2026 Weather Forecast for Japan: Temperatures May Be Above Normal

Table of Contents

Key Weather Forecast Points for Summer 2026 for the Energy Sector

According to the Japan Meteorological Agency’s warm-season forecast, summer 2026 (June–August) is expected to show a nationwide trend toward above-normal temperatures. The Pacific High is likely to extend toward Honshu, and after the end of the rainy season, the number of extremely hot days may increase across various regions.

In addition, the Japan Weather Association’s independent forecast indicates that in the previous year, the rainy season is expected to end early in 2026, leading to an earlier arrival of extreme heat.

From the perspective of the energy sector, the following three meteorological elements are particularly important to monitor this summer:

• Temperature (especially maximum temperature and nighttime temperatures)
• Solar radiation
• Extreme weather events such as typhoons

Temperature

Temperatures are expected to be above normal nationwide, with particularly severe heat anticipated in western and eastern Japan after the end of the rainy season. Nighttime temperatures are also expected to remain high.

As in the previous year, the early end of the rainy season and the early arrival of extreme heat may lead to an earlier-than-usual increase in cooling demand.

Solar Radiation

Total precipitation is expected to be generally near normal nationwide; however, there is a possibility of more frequent localized heavy rainfall during the rainy season.

During this period, increased cloudiness and rainfall may lead to significant variability in sunshine conditions across regions and time periods, which could affect solar power generation and electricity demand patterns.

Typhoons

In the latter half of summer, the Pacific High may temporarily weaken slightly, increasing the likelihood of typhoons approaching Japan. Strong winds, heavy rainfall, and associated temperature drops caused by typhoons can have a significant impact on the electricity supply-demand balance, requiring careful attention.

It is also important to note that these meteorological trends are not uniform nationwide and may vary by region.
Below, we outline how these weather conditions may affect energy-related business decisions.

Electricity Demand (Peak Demand)

Electricity demand has a strong correlation with temperature. In summer in particular, electricity demand tends to increase as cooling demand rises with higher temperatures.

In the summer of 2026, an early end to the rainy season and a subsequent high-temperature trend are expected. If severe heat occurs after the rainy season, peak demand may occur earlier than usual. In addition, if nighttime temperatures remain high (tropical nights with minimum temperatures of 25°C or higher), continued use of air conditioning may cause demand to remain elevated.

For electricity supply-demand management and trading divisions, the following meteorological conditions are particularly important decision-making factors:

• Frequency of extremely hot days (maximum temperature of 35°C or higher)
• Levels of nighttime temperatures (minimum temperatures)
• Occurrence of rapid temperature increases (short-term demand fluctuations)
• Duration of high temperatures
• Regional temperature differences

In Japan, supply-demand conditions differ by power area. Therefore, it is important to understand regional temperature trends and the duration of heat, rather than relying on national averages.

Electricity demand forecasts based on these meteorological conditions directly impact supply-demand planning revisions, power procurement, and market trading decisions.

*[Japan Weather Association] Electric power demand forecasting

Renewable Energy Generation

Renewable energy generation is highly dependent on weather conditions and is therefore a key source of uncertainty on the supply side.

Solar Power Generation

Solar power generation is highly dependent on solar radiation. Under sunny conditions, daytime power generation increases, whereas under cloudy or rainy conditions, power generation tends to decrease.

In the summer of 2026, localized rainfall may increase during the rainy season. If sunshine conditions become unstable during this period, solar power generation may vary by region, potentially increasing output variability.

Solar power generation also exhibits distinct patterns by time of day:

• Daytime: Increased power generation leads to higher supply
• Evening onward: Power generation decreases, tightening supply-demand conditions.

This “daytime-evening supply-demand gap” is an important factor affecting supply-demand management and market prices.

Therefore, in renewable energy operations and supply-demand management, it is important not only to forecast solar radiation but also to understand the supply-demand balance and make operational decisions by considering the time-of-day characteristics of solar power output.

*[Japan Weather Association] Solar Radiation & Solar Power Output Forecast SYNFOS-solar (Only Available in Japanese)

Wind Power Generation and Typhoon Risk

Wind power output depends on wind speed; when winds are weak, power generation decreases. During typhoon approaches, wind turbines may be shut down to protect equipment, posing a risk of temporary reductions in power generation.

Furthermore, typhoons may affect transmission and distribution facilities and related infrastructure through strong winds and heavy rainfall, creating additional supply-side risks.

Because wind power is strongly influenced by weather conditions, highly accurate wind power output forecasts and weather forecasts are essential for improving power generation planning, supply-demand adjustment, and risk management.

*[Japan Weather Association] SYNFOS-wind, Wind Power Generation Output Forecasting Service

*[Japan Weather Association] ENeAPI, an API Service for the Energy Industry

Electricity Market Prices

Weather conditions affect both electricity demand and renewable energy generation and are therefore one of the factors driving fluctuations in electricity market prices.

For example, when cooling demand increases due to extreme heat, electricity demand rises. If supply-demand conditions tighten, market prices tend to increase. In particular, when extremely hot days persist, peak demand increases, making prices more prone to spikes.

On the other hand, when sunny conditions prevail and solar radiation is high, increased solar power output raises daytime electricity supply, which tends to lower market prices. However, conditions vary by time of day:

• Daytime: Increased solar power generation → prices tend to decrease
• Evening: Reduced solar power generation + high demand → prices tend to increase

In addition, when typhoons approach, fluctuations in the supply-demand balance due to strong winds or outages may increase price volatility.

In this way, weather conditions affect both electricity demand and supply, thereby influencing electricity market prices. Price forecasts that incorporate weather forecasts are therefore an important factor in electricity trading and procurement decisions.

*[Japan Weather Association] Price Forecasting (Electricity Market Price Forecasting)

Decision-Making Points by Weather Conditions

In the summer of 2026, combinations of weather conditions may significantly alter supply-demand dynamics and market movements in the energy sector.

It is particularly important to make decisions based not on a single meteorological factor, but on combinations of multiple conditions.
For example, even under extreme heat, supply-demand conditions and market prices differ significantly depending on whether sunny or cloudy conditions persist. Therefore, it is important to assess the impacts on supply-demand and prices under different weather scenarios.

Can Summer Weather Forecasts Be Used for Management Decisions? (Actions Companies Should Take)

For the summer of 2026, it is important to undertake advance preparations from the following perspectives:

• Review of electricity supply-demand plans
• Ensuring adequate supply-demand reserves under extreme heat conditions
• Assessment of variability risks in renewable energy generation
• Understanding of electricity market price volatility risks
• Preparation for potential facility impacts due to typhoon approaches

By combining weather forecasts with demand forecasts and power generation forecasts, more accurate supply-demand management and informed market decision-making can be achieved.

Industry-Specific Analysis and Service Introduction

JWA provides information and consulting services for the energy sector, including long-term weather forecasts of up to two years ahead, electricity market price forecasts, and renewable energy generation forecasts.

• Price Forecasting (Electricity Market Price Forecasting)
  Price Forecasting (Electricity Market Price Forecasting) is a service that forecasts spot market trading prices (system price and area prices) on the Japan Electric Power Exchange (JEPX), as well as supply-demand adjustment market prices (Tertiary Reserve Type 2) on the Electric Power Reserve Exchange (EPRX), and delivers the results online.
  Highly accurate price forecasts enable strategic power generation, procurement, and charge/discharge planning, supporting price maximization and stable operations for energy businesses.
• Electricity Demand Forecasting
  Electricity demand is strongly influenced by a variety of weather elements, including temperature, humidity, solar radiation, rainfall, and snowfall.
  By combining the expertise of professional meteorologists with artificial intelligence and machine learning analysis technologies, JWA provides highly accurate demand forecasting services.
• Solar Radiation & Solar Power Output Forecast (SYNFOS-solar) (Only Available in Japanese)
  SYNFOS-solar forecasts solar radiation and solar power output at 30-minute intervals up to 78 hours ahead. Through spatial statistical correction of forecast values it also provides solar radiation distribution forecasts (mesh forecasts) by power area.
• Wind Power Output Forecasting Service (SYNFOS- wind)
  SYNFOS-wind is a wind power output forecasting service provided by JWA. Using proprietary weather models and AI-based analysis technologies, it delivers highly accurate forecasts up to 20 days ahead, including offshore wind.
• ENeAPI, an API Service for the Energy Industry
  ENeAPI provides highly accurate weather information through a Web API. The Solar API provides estimates and forecasts on solar radiation and solar power output.
  The Energy Management API provides essential weather information for advanced energy management—from individual factories, buildings, and homes to microgrids, smart cities, and power-area-level systems—as well as various data to support strategic electricity trading.
• 2-Year Long-Term Weather Forecast (Only Available in Japanese)
  JWA has developed the industry’s first forecasting method that offers higher accuracy and longer forecast periods than the conventional approach. By understanding long-term trends in temperature, precipitation, and snowfall up to two years ahead, it is possible to optimize supply planning and fuel procurement costs.
  For more details on 2-Year Long-Term Weather Forecasts, please click: What are Long-Term Forecasts? JWA’s Proprietary “2-Year Long-Term Weather Forecast” and Its Business Applications Part 1 / Part 2

These services serve as a foundation for incorporating weather information into decision-making in areas such as electricity supply-demand management, renewable energy operations, and electricity trading.

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