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SunnyDays

ERA5 almanac — 8 years of real data

Kauai in December

Kauai in December: 84% of days see measurable rain, 70°F average high, 4% of days historically clear (n=248, ERA5 2018–2025).

Kauai in December is historically a poor month for sun: only 4% of days clear across 8 years (n=248, avg high 70°F). January is the clearest month for Kauai 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 Kauai 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 December

Clear-sky percentage for Kauai in December, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early December
1st–15th		 3% n=120 70°F
Late December
16th–end		 4% n=128 70°F
Full month average 4% n=248 70°F

Sunshine & warmth in December

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 Kauai in December. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early December
1st–15th		 36% n=120
Late December
16th–end		 23% n=128
Full month average 29% n=248
10.2 h median sunshine per day 78% of days exceed 8 h sunshine 84% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 4%. Sunshine-based “warm & sunny”: 29%. The 25-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

Kauai is historically almost never clear in December: only 4% of days meet the clear bar across 8 years (n=248). Come back in January if you want clear skies here. Plan entirely around indoor or overcast-friendly activities.

→ See all destinations in January — historically the best month for sun in Kauai.

Every month in Kauai

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

Historical clear-sky % for Kauai, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 5% n=248 All destinations →
February 2% n=226 All destinations →
March 2% n=248 All destinations →
April 1% n=240 All destinations →
May 0% n=248 All destinations →
June 2% n=240 All destinations →
July 0% n=248 All destinations →
August 0% n=248 All destinations →
September 0% n=240 All destinations →
October 1% n=248 All destinations →
November 2% n=240 All destinations →
December ← this page 4% n=248 All destinations →

Frequently asked

Does it rain in Kauai in December?

Yes, frequently. In Kauai, 84% of days in December 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 Kauai good for sun in December?

Not usually. Kauai is historically overcast in December: only 4% of days are clear (avg high 70°F, n=248 days, ERA5 2018–2025). January 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.