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SunnyDays

ERA5 almanac — 8 years of real data

Lanai in September

Lanai in September: 37% of days see measurable rain, 82°F average high, 16% of days historically clear (n=240, ERA5 2018–2025).

Lanai in September is historically a poor month for sun: only 16% of days clear across 8 years (n=240, avg high 82°F). January is the clearest month for Lanai 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 Lanai 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 Lanai 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		 20% n=120 82°F
Late September
16th–end		 12% n=120 82°F
Full month average 16% n=240 82°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 Lanai 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		 100% n=120
Late September
16th–end		 100% n=120
Full month average 100% n=240
11.8 h median sunshine per day 99% of days exceed 8 h sunshine 37% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 16%. Sunshine-based “warm & sunny”: 100%. The 84-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

Lanai is a poor choice for sun in September: just 16% of days clear historically (n=240). January 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 January — historically the best month for sun in Lanai.

Every month in Lanai

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

Historical clear-sky % for Lanai, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 32% n=248 All destinations →
February 19% n=226 All destinations →
March 20% n=248 All destinations →
April 14% n=240 All destinations →
May 17% n=248 All destinations →
June 20% n=240 All destinations →
July 20% n=248 All destinations →
August 26% n=248 All destinations →
September ← this page 16% n=240 All destinations →
October 20% n=248 All destinations →
November 31% n=240 All destinations →
December 27% n=248 All destinations →

Frequently asked

Does it rain in Lanai in September?

Sometimes. Lanai sees measurable rain on 37% of days in September historically (n=240 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Lanai good for sun in September?

Not usually. Lanai is historically overcast in September: only 16% of days are clear (avg high 82°F, n=240 days, ERA5 2018–2025). January is historically far better for sun here.

How Lanai compares in September

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