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How Sun Season judges the weather

the same rules run on the map, on every destination page and in the where-to-go lists

temperature in · rain in · distances in — tap a unit to switch.

Sun Season answers one question for any place and month: does the climate fit the holiday you want? It takes 30-year monthly averages of rainfall and mean temperature (WorldClim 2.1, 1970–2000), sorts each month into a rain class and a temperature band, and compares both with a preset such as Beach or Snow. The result is a verdict — good, too cold, too hot, too dry, too rainy or monsoon — for every 0.25° cell of land on Earth, for each of the twelve months.

Rain classes

Raw millimetres mislead: 200 mm in a month is ordinary in Singapore and a monsoon in Goa. Each month is classed relative to that place's own year, where P_max and P_min are its wettest and driest months:

Class	Rule
monsoon	≥ 180 mm7.1 in (or ≥ 120 mm4.7 in when that is ≥ 80 % of P_max), and the climate is seasonal: P_max ≥ 3 × P_min
rainy	≥ 100 mm3.9 in and ≥ 35 % of P_max
showers	≥ 60 mm2.4 in
dry	everything else

So a place that is wet all year (New Zealand's west coast, Singapore) reads as rainy, not monsoon; monsoon is reserved for heavy rain that arrives as a season.

Temperature bands

Mean monthly temperature, in five steps: freeze below 0 °C32 °F · cool 0–14 °C32–57 °F · warm 14–24 °C57–75 °F · hot 24–33 °C75–91 °F · burn above 33 °C91 °F. These are monthly means, so a "hot" month has afternoons well above its number.

Presets

Preset	Rule
Warm	mean 14–24 °C57–75 °F, dry or showers
Tropical	mean 24–33 °C75–91 °F, anything but the monsoon
Beach	mean 24–33 °C75–91 °F, dry or showers
Cool	mean 0–14 °C32–57 °F, anything but the monsoon
Snow	mean below 0 °C32 °F, any rain

A month fits when its temperature band is inside the preset's range and its rain class is not above it. The verdict names the first failing reason: temperature first (too cold, too hot), then rain (too dry, too rainy, monsoon). Destination pages use the Tropical preset between the tropic lines and Warm elsewhere; the map lets you pick any range.

Data

Rainfall and temperature are WorldClim 2.1 monthly normals for 1970–2000 at 2.5 arc-minutes, aggregated to a 0.25° grid (about 28 km17 mi at the equator). Place names and coordinates come from GeoNames. Everything is served as static files — see the data page.

What this cannot tell you

It is a climate, not a forecast. A 30-year average says what a month is usually like, not what next week will be.
Cells are 0.25° wide. Mountains, coasts and islands smaller than that inherit their surroundings; a page says "nearest land cell" when the exact point is sea.
1970–2000 is the baseline. Recent decades run warmer; treat temperature bands as slightly conservative.
Means hide extremes. A dry month can still have a storm; a rainy month can still have sunny mornings.

Who made this

Sun Season is built and maintained by Lauren ten Hoor, a software engineer in the Netherlands, as an independent side project. It began as "Monsoon?", a map to settle the question of whether a place is in its rainy season, and still runs at monsoon.s3p.dev.