Japan’s Latest Summer 2026 Outlook | Midsummer Heat from Mid-July: Caution Advised for Temperatures of 40°C or Higher, Thunderstorms, and Typhoon Risks

2026.07.29

Heat and rain are expected to be the defining features of summer 2026.

Dangerously high temperatures of 40°C or higher may occur locally due to factors such as strong sunshine after the end of the rainy season and foehn winds associated with approaching typhoons.

Even after the rainy season ends, the weather is not expected to remain stable, and localized showers and thunderstorms may become more frequent, mainly in eastern and western Japan.
In August, the weather is expected to change frequently due to the influence of typhoons and moist air.

For business operations, it is important to monitor not only high temperatures but also sudden thunderstorms, short-duration heavy rain, and the risks of heavy rain and extreme heat associated with approaching typhoons.

This article explains the outlook for heat, the risk of temperatures reaching 40°C or higher, and the risks of rain, thunderstorms, and typhoons in the midsummer period of 2026, as well as key points to consider in operational decision-making.

For more information on the characteristics of summer weather in Japan, see: Summer Weather in Japan: What Global Businesses Need to Know (Beyond Travel Tips)

Table of Contents

Key Points of the 2026 Midsummer Outlook | Heat After the Rainy Season and Thunderstorm and Typhoon Risks

The key points of the 2026 midsummer outlook are heat, thunderstorms, and typhoons.

Key Point 1: Heat

• After the rainy season ends, midsummer heat is expected, with some inland areas likely to experience days with daily maximum temperatures of 35°C or higher from late July to early August.
• Particular caution is required when strong sunshine continues after the rainy season ends and when foehn winds occur on the Sea of Japan side as a typhoon approaches.
• Temperatures may locally reach 40°C or higher in areas where the necessary weather conditions coincide.

For an explanation of Japan’s rainy season, see: What Is Japan’s Baiu, or Tsuyu, Rainy Season? Explaining the Mechanism of Baiu and “Onset of Baiu” / “End of Baiu”

Key Point 2: Thunderstorms and Typhoons

• Even after the rainy season ends, the weather is not expected to remain stable. Localized rain and thunderstorms are likely to occur, particularly on the Pacific side, due to the influence of typhoons and moist air.
• In August, the weather is expected to change frequently due to the influence of typhoons and moist air.

For more information on typhoons and heavy rain in Japan, see: Typhoons and Heavy Rain in Japan: Business Risks for Global Companies and the Use of Weather Data Part 1 / Part 2

Feature 1 of the 2026 Midsummer Outlook: Heat

In summer 2026, intense heat is expected after the rainy season ends.

For corporate heat countermeasures, it is important to monitor not only the risk of temperatures reaching 40°C or higher, but also the timing and areas in which temperatures are likely to rise sharply.

When using forecasts for business operations, it is important not only to determine whether temperatures will reach 40°C, but also to identify in advance the possibility of dangerously high temperatures.

For summer 2026, it is important to identify areas where temperatures may approach 40°C and periods when temperatures are likely to rise sharply, such as after the rainy season ends or when a typhoon approaches, and to take preventive measures in advance.

Two Periods Requiring Particular Caution for Temperatures of 40°C or Higher: (1) After the Rainy Season Ends and (2) When a Typhoon Approaches

The two periods requiring particular caution for extreme heat are after the rainy season ends, when strong sunshine continues, and when foehn winds occur as a typhoon approaches.

1. Caution Required for Strong Sunshine After the Rainy Season Ends

After the rainy season ends, the Pacific High extends toward Honshu, and consecutive sunny days with strong sunshine cause heat to accumulate near the ground, causing temperatures to rise day by day. If warm air also flows in aloft, temperatures are likely to rise across a wide area.

In particular, inland areas and basins in the Kanto and Tokai regions tend to become very hot because they are less affected by sea breezes and heat is more likely to build up. Temperatures may also locally reach 40°C or higher in inland areas of the Kinki and Chugoku regions and in basins in Shikoku when several conditions coincide.

From mid-July onward, when the rainy season is expected to end, midsummer heat is likely, and some inland areas may experience days with daily maximum temperatures of 35°C or higher from late July to early August.

2. Caution Required for Foehn Winds When a Typhoon Approaches

When a typhoon approaches, the risk of temperatures reaching 40°C or higher may increase, particularly on the Sea of Japan side.

This summer, the Pacific High is expected to weaken temporarily at times, making it easier for typhoons to approach Japan. As a result, the number of typhoons approaching Japan is expected to be near or above normal, particularly in August.

*Related article
For details of the typhoon outlook, see: Japan’s 2026 Typhoon Outlook: Increased Risk of Typhoons Approaching Japan in August, with Potential Impacts from Stronger Typhoons in Autumn

When a typhoon approaches Japan, depending on its track and wind direction, a foehn effect may occur as winds around the typhoon cross mountainous terrain and descend, potentially causing high temperatures, particularly on the Sea of Japan side.

For example, when a typhoon approached and made landfall in Japan on August 14–15, 2019, typhoon-related foehn winds contributed to daily maximum temperatures of 40°C or higher at multiple locations in Niigata and Ishikawa prefectures.

Due to foehn winds, dangerously high temperatures of 40°C or higher may occur locally, particularly in the Hokuriku region. In northern Kinki and the San’in region as well, temperatures may rise sharply if conditions such as the typhoon’s track, wind direction, mountainous terrain, and strong sunshine coincide.

Even on the Sea of Japan side, where temperatures of 40°C or higher were not frequently observed in 2025, caution is required in 2026 for sharp temperature increases caused by foehn winds when typhoons approach.

*For more information on the mechanism of foehn winds and corporate heat countermeasures, see: What Is the Foehn Phenomenon? Localized Extreme Heat Risks and Heat Countermeasures for Businesses (only available in Japanese)

Risk of Temperatures Reaching 40°C or Higher by Region

Temperatures of 40°C or higher tend to be observed in inland areas, basins, and mountainous areas of eastern and western Japan.

Based on past trends in temperatures of 40°C or higher and the expected atmospheric conditions, the risk in 2026 is expected to be high in eastern Japan and somewhat high in western Japan.

*About the risk levels

High: Areas with many past cases of temperatures reaching 40°C or higher and where similar conditions are likely to occur in 2026

Somewhat high: Areas with past cases of temperatures reaching 40°C or higher where similar conditions could occur in 2026.

Moderate: Areas where temperatures may rise locally depending on conditions.

Somewhat low: Areas where temperatures are relatively unlikely to reach 40°C or higher, but caution is still required for extreme heat and humid conditions.

Feature 2 of the 2026 Midsummer Outlook: Rain, Thunderstorms, and Typhoon risks

In summer 2026, the weather conditions are expected to remain changeable even after the rainy season ends due to fluctuations in the Pacific High and the influence of typhoons and moist air. While high temperatures are expected to continue, caution is also required for localized showers and thunderstorms, as well as heavy rain when typhoons approach.

Continued Caution for Rain Even After the Rainy Season Ends

The risk of heavy rain does not disappear once the rainy season ends. Although sunshine duration is expected to increase and temperatures are forecast to remain high nationwide after the rainy season, showers and thunderstorms may become more frequent in eastern and western Japan.

From August Onward, Caution Also Required for Heavy Rain and High Temperatures Associated with Approaching Typhoons

From early to mid-August, there will be periods of sunny weather, but the Pacific High is expected to weaken at times. As a result, the weather conditions are likely to become more variable under the influence of typhoons and moist air, bringing hot and humid conditions across the country.

According to JWA’s forecast, the number of typhoons approaching Japan is expected to be near or above normal, particularly in August. Businesses should therefore prepare for heavy rain, typhoons, and potential impacts on logistics and operations.

For the detailed typhoon outlook, see: Japan’s 2026 Typhoon Outlook: Increased Risk of Typhoons Approaching Japan in August, with Potential Impacts from Stronger Typhoons in Autumn

In 2026, it will be important to continue monitoring information on typhoon formation and approaches even after the midsummer period.

Key Decision-Making Points for Businesses in the 2026 Midsummer Period

For business operations, it is important to continue monitoring not only temperatures and sunshine duration but also thunderstorms, short-duration heavy rain, typhoons, and moist-air conditions.

How to Use Midsummer Heat, Rain, and Typhoon Risks in Business Decision-Making

During the midsummer period, it is important to review not only long-term temperature trends but also shorter-range forecasts and typhoon information.

For business decisions, the following types of information should be considered in combination.

The weather data that should be monitored for midsummer heat, thunderstorms, and typhoon risks differ depending on the industry and business location.
JWA can provide support tailored to each company’s needs, from the provision of weather data to its use in demand forecasting and risk-based decision-making. Please feel free to contact us.

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