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SunnyDays

ERA5 almanac — 8 years of real data

San Juan Islands in August

San Juan Islands in August: 14% of days see measurable rain, 70°F average high, 27% of days historically clear (n=248, ERA5 2018–2025).

San Juan Islands in August is historically a poor month for sun: only 27% of days clear across 8 years (n=248, avg high 70°F). Historical average, not a forecast.

What you are reading: 8-year historical averages from the ERA5 reanalysis, not a forecast. A month that is historically 90% clear can still be overcast on your specific trip. For this week’s actual forecast, see the live San Juan Islands page. Both can be true at once: “historically strong in this month; this particular week is not.” We label which is which.

Early vs. Late August

Clear-sky percentage for San Juan Islands in August, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early August
1st–15th		 33% n=120 70°F
Late August
16th–end		 22% n=128 70°F
Full month average 27% n=248 70°F

Sunshine & warmth in August

A second measure using actual sunshine hours (ERA5 sunshine_duration), not the daily weather code. A Lowcountry day with 12 hours of sun and a 25-minute afternoon storm is counted below as a warm, sunny day — because it was. How we define this.

Sunshine-based metrics for San Juan Islands in August. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early August
1st–15th		 36% n=120
Late August
16th–end		 24% n=128
Full month average 30% n=248
13.4 h median sunshine per day 91% of days exceed 8 h sunshine 14% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 27%. Sunshine-based “warm & sunny”: 30%.

Bottom line

San Juan Islands is mostly overcast in August historically: only 27% of days are clear across 8 years (n=248), avg high 70°F. Most visitors this month will see more clouds than sun.

Every month in San Juan Islands

Compare across all months with data. Numbers are historical clear-sky %.

Historical clear-sky % for San Juan Islands, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 0% n=248 All destinations →
February 0% n=226 All destinations →
March 0% n=248 All destinations →
April 0% n=240 All destinations →
May 3% n=248 All destinations →
June 10% n=240 All destinations →
July 26% n=248 All destinations →
August ← this page 27% n=248 All destinations →
September 6% n=240 All destinations →
October 1% n=248 All destinations →
November 0% n=240 All destinations →
December 0% n=248 All destinations →

Frequently asked

Does it rain in San Juan Islands in August?

Rarely. Only 14% of days in San Juan Islands see measurable rain in August, based on 8 years of ERA5 historical data (n=248 days, 2018–2025). This is a historical average, not a forecast.

Is San Juan Islands good for sun in August?

Not usually. San Juan Islands is historically overcast in August: only 27% of days are clear (avg high 70°F, n=248 days, ERA5 2018–2025).

How San Juan Islands compares in August

Head-to-head clear-sky comparisons against destinations travelers plausibly weigh against San Juan Islands this month — same passport tier, similar flight distance, both sides from the same 8-year ERA5 record.

All percentages are historical averages from the ERA5 reanalysis via Open-Meteo, 8 full years (2018–2025). “Clear” means avg high ≥ 72 °F, precipitation < 1 mm, and a non-precipitation weather code. This is history, not a forecast. The live 7-day outlook for any destination is on its own page and may differ from the long-run average. Data from Open-Meteo.