What this solves
Tokyo summer is famously hot: 35°C + 70% humidity = Humidex 49°C, very uncomfortable. Heat stroke is the #1 cause of tourist death in summer. Riviera weather averages 25°C in August, but feels hotter. This calculator gives a Humidex score + general safety advice. We also cover tsuyu (rainy season, June–mid-July) and typhoon season (late June–October).
Compute
How to read results
- Humidex < 29: comfortable.
- 29–39: some discomfort. Stay hydrated.
- 40–45: great discomfort. Avoid midday outdoor activity.
- 46+: heat stroke risk. Stay indoors.
- Heat-illness symptoms: dizziness, headache, no sweat, cramps. Move to AC room; cool with cold water + fan; salt-free see doctor.
- Tsuyu: plum-rain front June 7–July 20 (Tokyo). 50% chance of rain daily. Carry umbrella always.
Limitations
Reference for 2026. Humidex is one of many indices (WBGT is the official metric used in Japan). Tokyo heat is generally 1-3°C hotter than rural areas.
FAQ
How hot does Tokyo actually get?
Summer highs 32-35°C; feels like 40+ with humidity. Record 41°C (2023).
What's the typhoon season?
Late June to October. Most active August-September. Kansai/affected areas should check airfares daily.
What to pack in winter?
Layer with warm-up fleece. Tokyo/Kyoto winter is -3 to 10°C. Hokkaido goes to -15°C.
About this tool
Purpose: estimate heat-stroke risk. Scope: Japan summer + general climate. Not a medical tool.
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Disclaimer
Reference for 2026. For medical emergency, call 119.