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SunnyDays

ERA5 almanac — 8 years of real data

Jacksonville in September

Jacksonville in September: 58% of days see measurable rain, 86°F average high, 22% of days historically clear (n=240, ERA5 2018–2025).

Jacksonville in September is historically a poor month for sun: only 22% of days clear across 8 years (n=240, avg high 86°F). April is the clearest month for Jacksonville 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 Jacksonville 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 Jacksonville 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		 17% n=120 86°F
Late September
16th–end		 27% n=120 86°F
Full month average 22% n=240 86°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 Jacksonville 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		 88% n=120
Full month average 88% n=240
11.2 h median sunshine per day 82% of days exceed 8 h sunshine 58% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 22%. Sunshine-based “warm & sunny”: 88%. The 66-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

Jacksonville is mostly overcast in September historically: only 22% of days are clear across 8 years (n=240), avg high 86°F. If you want sun in Jacksonville, April is historically much better. Most visitors this month will see more clouds than sun.

→ See all destinations in April — historically the best month for sun in Jacksonville.

Every month in Jacksonville

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

Historical clear-sky % for Jacksonville, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 9% n=248 All destinations →
February 27% n=226 All destinations →
March 37% n=248 All destinations →
April 48% n=240 All destinations →
May 41% n=248 All destinations →
June 15% n=240 All destinations →
July 8% n=248 All destinations →
August 7% n=248 All destinations →
September ← this page 22% n=240 All destinations →
October 33% n=248 All destinations →
November 24% n=240 All destinations →
December 16% n=248 All destinations →

Frequently asked

Does it rain in Jacksonville in September?

Yes, frequently. In Jacksonville, 58% of days in September see measurable rain, based on 8 years of ERA5 historical data (n=240 days, 2018–2025). This is a historical average, not a forecast.

Is Jacksonville good for sun in September?

Not usually. Jacksonville is historically overcast in September: only 22% of days are clear (avg high 86°F, n=240 days, ERA5 2018–2025). April is historically far better for sun here.

How Jacksonville compares in September

Head-to-head clear-sky comparisons against destinations travelers plausibly weigh against Jacksonville 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.