Japan weather by month

In Tokyo, the average share of the sky covered by clouds shows significant seasonal variation over the course of the year.

The clearer part of the year begins around October 19 and lasts for 5.6 months, ending around April 5. The clearest month is January, when the sky is clear, mostly clear, or partly cloudy 72% of the time on average.

The cloudier part of the year begins around April 6 and lasts for 6.4 months, ending around October 18. The cloudiest month is June, when it is overcast or mostly cloudy 78% of the time.

This is the average sustained wind speed at the standard 10 metres above open ground — the steady flow a weather station reports, not the sharper gusts that come and go, which can run half again as fast. It's the number that says whether a place is generally breezy or calm.

Across the year, average wind speed in Tokyo is typically light breeze, near 12 km/h, and varies little with the seasons.

The windier part of the year lasts 4.5 months, from around Jan 13 to May 30. The windiest month is April, averaging about 14 km/h (light breeze).

The calmer part of the year runs from around May 31 to Jan 12, with November the calmest month at about 11 km/h.

Solar energy is how much sunlight actually reaches the ground each day, measured in kilowatt-hours per square metre (kWh/m²) — the combined effect of how long the sun is up, how high it climbs, and how much cloud gets in the way. It's the raw fuel a solar panel has to work with: for scale, 1 kWh/m² a day is dim and wintry, while 7+ is desert-bright.

Tokyo receives about 3.8 kWh/m² a day of solar energy on average — moderate — with a clear seasonal swing between 2.3 and 5.1 kWh/m².

The brighter stretch of the year lasts 6.3 months, from around Mar 5 to Sep 11. The brightest month is May, averaging about 5.1 kWh/m² (bright).

The dimmest month is December, down near 2.4 kWh/m² — roughly 53% less than the May peak.