Residual Heat in September 2025: How Different Is It from Last Year?

Residual heat in September 2025

Autumn on the Calendar... But the Heat Persists

September usually brings the feeling of autumn, yet in 2025 forecasts still show midsummer-like days above 30°C across Japan.
How does this compare to last year’s record-breaking residual heat? Let’s break it down using weather data.

In this article, we’ll cover:

September 2025 temperature trends
The difference from 2024
Practical lifestyle tips to beat the lingering heat

Weather Outlook for September 2025

The Japan Weather Association projects above-average temperatures, with midsummer days (30–34°C) continuing nationwide through September.
From the Tokai region to Okinawa, conditions are at a "Severe Heat Alert Level", while Kanto and Hokuriku are under "Heat Alert Level".
In Tokyo, maximum temperatures are forecast to fall below 30°C only from mid-September, suggesting that the heat will linger well into the month.

Here’s the forecast trend visualized:

Temperature forecast for September 2025

Although not as extreme as last year, 2025 still shows a clear pattern of prolonged heat above normal levels.

Looking Back: September 2024 Was “Extraordinary”

Last year (September 2024) was exceptional, marking one of the hottest on record:

Osaka and Sakai exceeded 37°C, the highest ever recorded in September.
The number of extremely hot days (35°C or higher) reached a record high.
Heatstroke cases surged, and the summer was widely labeled as abnormal weather.

2025 vs. 2024: What’s Different About the Heat?

2024: Extraordinary, with repeated days of “extreme heat” rather than just midsummer levels.
2025: Still hotter than average, but fewer extreme records. There are hints of an eventual return to autumn.

In short: better than last year, but not safe to let your guard down.

3 Practical Tips to Cope with Lingering Heat

Stay hydrated and replenish salt
→ Make hydration a habit, especially in the cooler hours of the morning and evening.
Use air conditioning wisely
→ Combine with timers or circulators to avoid overcooling while keeping rooms comfortable.
Improve your sleep environment
→ Opt for breathable bedding and cooling items to rest well, even during tropical nights.

Conclusion

Even if 2025 doesn’t reach the extremes of 2024, September remains a month of heat worth watching carefully.
Understanding the data is the first step to effective countermeasures. Try incorporating these tips into your daily routine to protect your health.