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SunnyDays

ERA5 almanac — 8 years of real data

St. Augustine in September

St. Augustine in September is historically a poor month for sun: only 17% of days clear across 8 years (n=240, avg high 83°F). April is the clearest month for St. Augustine 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. Augustine 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 September

Clear-sky percentage for St. Augustine in September, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early September
1st–15th		 11% n=120 83°F
Late September
16th–end		 23% n=120 83°F
Full month average 17% n=240 83°F

Sunshine & warmth in September

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. Augustine in September. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early September
1st–15th		 89% n=120
Late September
16th–end		 87% n=120
Full month average 88% n=240
11.2 h median sunshine per day 83% of days exceed 8 h sunshine 64% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 17%. Sunshine-based “warm & sunny”: 88%. The 71-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. Augustine is a poor choice for sun in September: just 17% of days clear historically (n=240). April 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 April — historically the best month for sun in St. Augustine.

Every month in St. Augustine

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

Historical clear-sky % for St. Augustine, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 9% n=248 All destinations →
February 22% n=226 All destinations →
March 25% n=248 All destinations →
April 42% n=240 All destinations →
May 40% n=248 All destinations →
June 14% n=240 All destinations →
July 9% n=248 All destinations →
August 6% n=248 All destinations →
September ← this page 17% n=240 All destinations →
October 34% n=248 All destinations →
November 23% n=240 All destinations →
December 13% n=248 All destinations →

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.