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SunnyDays

ERA5 almanac — 8 years of real data

St. John, USVI in August

St. John, USVI in August: 51% of days see measurable rain, 80°F average high, 13% of days historically clear (n=248, ERA5 2018–2025).

St. John, USVI in August is historically a poor month for sun: only 13% of days clear across 8 years (n=248, avg high 80°F). March is the clearest month for St. John, USVI historically. 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 St. John, USVI 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 St. John, USVI 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		 10% n=120 80°F
Late August
16th–end		 16% n=128 80°F
Full month average 13% n=248 80°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 St. John, USVI 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		 97% n=120
Late August
16th–end		 95% n=128
Full month average 96% n=248
12.2 h median sunshine per day 94% of days exceed 8 h sunshine 51% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 13%. Sunshine-based “warm & sunny”: 96%. The 83-point gap is from brief afternoon convective storms that stamp the whole day as “rain” in the WMO code but leave the bulk of the sunshine untouched.

Bottom line

St. John, USVI is a poor choice for sun in August: just 13% of days clear historically (n=248). March is the historically strongest month for sun here. The 8-year record is consistent — this is not a fluke bad stretch.

→ See all destinations in March — historically the best month for sun in St. John, USVI.

Every month in St. John, USVI

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

Historical clear-sky % for St. John, USVI, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 18% n=248 All destinations →
February 13% n=226 All destinations →
March 28% n=248 All destinations →
April 20% n=240 All destinations →
May 25% n=248 All destinations →
June 20% n=240 All destinations →
July 9% n=248 All destinations →
August ← this page 13% n=248 All destinations →
September 15% n=240 All destinations →
October 15% n=248 All destinations →
November 18% n=240 All destinations →
December 16% n=248 All destinations →

Frequently asked

Does it rain in St. John, USVI in August?

Yes, frequently. In St. John, USVI, 51% of days in August see measurable rain, based on 8 years of ERA5 historical data (n=248 days, 2018–2025). This is a historical average, not a forecast.

Is St. John, USVI good for sun in August?

Not usually. St. John, USVI is historically overcast in August: only 13% of days are clear (avg high 80°F, n=248 days, ERA5 2018–2025). March is historically far better for sun here.

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.