As autumn approaches, Japan is no stranger to fluctuating weather patterns, but the latest forecast from the Japan Meteorological Agency (JMA) has caught widespread attention. On September 8, 2025, the JMA announced an “Early Weather Information on High Temperatures,” warning of unusually elevated temperatures across the entire country starting around September 14. This alert highlights a potential heat event on a “once-in-10-years” scale, where temperatures could significantly exceed seasonal norms.
This comes on the heels of what has been described as Japan’s hottest summer on record, with sweltering conditions persisting well into September. According to recent forecasts, there’s an 80% chance of above-average temperatures nationwide during this period. Regions from the northern island of Hokkaido to the subtropical Okinawa are all included, emphasizing the widespread nature of this weather phenomenon. In this blog post, we’ll break down the details of the alert, its implications, and practical tips to help you navigate the heat—whether you’re a local or visiting from abroad.
Understanding the JMA’s High-Temperature Early Weather Information
The JMA’s “Early Weather Information on High Temperatures” is a proactive advisory issued when there’s a heightened probability of significantly above-average temperatures in the coming days. Specifically, it’s triggered when the likelihood of “considerably high” temperatures—defined as a 5-day average temperature deviation from the norm—reaches 30% or higher for the period 6 to 14 days ahead. As explained by the Japan Meteorological Association, such events are rare, occurring only about once every decade, making this alert a call for heightened awareness.
In this case, the forecast points to warm air masses enveloping Japan, prolonging the high temperatures that have already dominated the past week or more in most areas. If the heat intensifies within a week, the JMA may issue further “High-Temperature Weather Information.” For immediate risks, a “Heatstroke Alert” could be announced the day before or on the day of extreme conditions. This tiered system reflects Japan’s meticulous approach to weather monitoring, prioritizing public health and safety in a country where summer heat can be intense due to high humidity levels.
Regions Affected and Temperature Expectations
The alert covers all major regions of Japan, each with its own criteria for what constitutes “considerably high” temperatures based on historical data. Here’s a breakdown:
- Hokkaido: Starting around September 14, expect a 5-day average temperature at least 2.2°C above normal. Recent warm spells are set to continue under persistent warm air influence.
- Tohoku: Similar timeline, with deviations of +2.5°C or more. The region has seen elevated temperatures for over a week, and forecasts suggest many hot days ahead.
- Kanto-Koshin: Anticipate +2.6°C above average. This densely populated area, including Tokyo, has been warm recently, and the trend is expected to persist.
- Hokuriku: +2.8°C deviation. Warm conditions ongoing, with warm air likely to dominate the next two weeks.
- Tokai: +2.1°C above norm. Recent highs continue, potentially leading to numerous hot days.
- Kinki (Kansai): +2.3°C. Areas like Osaka and Kyoto may see prolonged warmth.
- Chugoku: +2.6°C. Expect many days of high temperatures due to lingering warm air.
- Shikoku: +1.9°C. The region has been hot for over a week, with forecasts indicating continuation.
- Kyushu Northern (including Yamaguchi Prefecture): +2.2°C. Similar patterns of recent and upcoming heat.
- Kyushu Southern and Amami: +1.6°C. Warm conditions expected to prevail.
- Okinawa: +1.1°C above average. As a subtropical zone, even small deviations can feel intense.
These regional variations account for Japan’s geographical diversity, from cooler northern latitudes to warmer southern islands. Overall, daytime highs could reach 27°C (80.6°F) on average, dropping to around 20°C (68°F) at night, but with humidity, it may feel much hotter. This extension of summer-like weather into September aligns with broader patterns observed this year, where record-breaking heat has already strained resources.
Health and Agricultural Implications
The primary concern with this heat surge is the increased risk of heatstroke, a serious condition exacerbated by Japan’s humid climate. The JMA urges everyone to take precautions during outdoor activities: ensure ample drinking water, seek shade frequently, and monitor health closely. Vulnerable groups, such as the elderly, children, and those with pre-existing conditions, should be particularly cautious.
Beyond human health, the alert highlights risks to agriculture and livestock. Farmers are advised to manage crops and animals carefully, as prolonged heat can affect yields and animal welfare. In a country where agriculture is integral to culture and economy—think rice paddies in Tohoku or tea plantations in Kyushu—these warnings help mitigate potential losses.
Tips for Staying Safe and Enjoying Japan During the Heat
If you’re traveling to Japan in mid-September 2025, don’t let the heat deter you—autumn festivals like Tsukimi (moon viewing) are just around the corner, offering cultural highlights amid milder evenings. To stay comfortable:
- Wear lightweight, breathable clothing and use hats or umbrellas for sun protection, a common practice in Japan.
- Stay hydrated with water or Pocari Sweat, a popular electrolyte drink available at convenience stores like 7-Eleven.
- Plan indoor activities during peak heat hours, such as visiting museums in Tokyo or onsen (hot springs) in cooler mountainous areas.
- Download apps like the JMA’s weather radar or Yahoo! Weather for real-time updates.
Frequently Asked Questions (FAQs)
1. What exactly is the JMA’s “Early Weather Information on High Temperatures”?
This is an advisory issued 6-14 days in advance when there’s a 30% or higher chance of significantly above-average temperatures, occurring roughly once every 10 years. It aims to promote early preparation for heat-related risks.
2. Which parts of Japan are most affected by the September 2025 heat alert?
The alert spans the entire country, from Hokkaido in the north to Okinawa in the south, with varying temperature deviation thresholds tailored to each region’s climate norms.
3. How can I prevent heatstroke while in Japan during this period?
Key measures include staying hydrated, avoiding direct sunlight during midday, wearing light clothing, and using air-conditioned spaces. Monitor for symptoms like dizziness and seek medical help if needed.
4. Is this heat surge linked to climate change?
While the JMA doesn’t explicitly connect individual events to climate change, global trends show increasing frequency of extreme heat. Japan’s record-hot summer of 2025 supports observations of warming patterns worldwide.
Final Thoughts
As Japan prepares for this unusual mid-September heat in 2025, the JMA’s timely alert underscores the value of proactive weather communication. Whether you’re a resident managing daily routines or an international visitor exploring temples and cities, prioritizing safety will ensure a positive experience. Safe travels!
