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Best time to visit · Washington, United States
On the climate data, the best time to visit San Juan Island is June – September, scoring up to 95/100 with highs around 70°F (21°C) and 0.7 in (18 mm) of rain in July. May is a good shoulder-season month. The toughest months are December & January, mainly because of cloud cover.
Highs run from 44°F to 70°F across the year, and the yearly total is about 39.0 in (991 mm) of rain.
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high | 45°F7°C | 46°F8°C | 49°F9°C | 53°F12°C | 60°F15°C | 64°F18°C | 70°F21°C | 70°F21°C | 65°F18°C | 56°F13°C | 49°F9°C | 44°F7°C |
| Avg low | 39°F4°C | 39°F4°C | 41°F5°C | 44°F7°C | 49°F9°C | 53°F11°C | 56°F13°C | 57°F14°C | 54°F12°C | 48°F9°C | 43°F6°C | 39°F4°C |
| Rain | 5.8 in147 mm | 3.3 in84 mm | 4.2 in106 mm | 2.8 in70 mm | 2.0 in52 mm | 1.5 in37 mm | 0.7 in18 mm | 1.1 in27 mm | 2.0 in50 mm | 4.3 in109 mm | 6.1 in154 mm | 5.4 in137 mm |
| Humidity | 87% | 83% | 82% | 80% | 79% | 78% | 75% | 74% | 77% | 83% | 86% | 86% |
| Cloud | 83% | 76% | 79% | 73% | 67% | 64% | 44% | 46% | 54% | 70% | 79% | 83% |
| Comfort | 37 | 48 | 50 | 63 | 78 | 87 | 95 | 95 | 91 | 64 | 44 | 37 |
Source: NASA POWER (public domain), 2001–2025 monthly averages on a ~50 km satellite and reanalysis grid, so coasts and valleys can differ from what's shown. The grid cell sits at about 52 m (171 ft), close to San Juan Island's own ~18 m. Precipitation includes snow as melted water; daylight is calculated from latitude. Check a forecast before you go.
The coldest season, with highs of 44–46°F (7–8°C) and lows down to 39°F (4°C). It's the wettest season, with about 14.5 in (368 mm) of rain, 37% of the year's total. It holds the toughest stretch on our comfort score (December & January), averaging 41/100.
Temperatures climb through the season, from 49°F highs in March to 60°F by May. About 9.0 in (228 mm) of rain falls across these months, 23% of the year's total. Lows bottom out around 41°F (5°C). May score well without being the very best (season average 64/100).
Peak warmth: highs of 64–70°F (18–21°C). It's the driest season, with only about 3.2 in (82 mm) of rain, 8% of the year's total. Lows bottom out around 53°F (11°C). June – August are among the best-scoring months (season average 92/100).
Temperatures slide from 65°F highs in September to 49°F by November. About 12.3 in (313 mm) of rain falls across these months, 32% of the year's total. Lows bottom out around 43°F (6°C). Comfort peaks here: September ranks with the year's best, and the season averages 66/100.
By comfort score: 5 Great, 2 Good, 2 Fair and 3 Tough. Great months: May – September. Tap a month for its own guide.
On the climate data, the best time to visit San Juan Island is June – September, scoring up to 95/100 with highs around 70°F (21°C) and 0.7 in (18 mm) of rain in July. May is a good shoulder-season month. The toughest months are December & January, mainly because of cloud cover.
November is the wettest month, averaging about 6.1 in (154 mm) of rain. July is the driest, with about 0.7 in (18 mm). The yearly total is around 39.0 in (991 mm).
February is the coldest, with average lows of 39°F (4°C) and highs of 46°F (8°C). The warmest is August, with average highs of 70°F (21°C).
Not very: summer (June – August) humidity averages 76%, and highs peak around 70°F (21°C), so it rarely feels sticky.
Not on average: even in February, the coldest month, lows average 39°F (4°C). Individual cold snaps can still dip lower.
Poll the group on June – September dates, then plan the days, packing and costs together.
