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SunnyDays

ERA5 almanac — 8 years of real data

Kauai in May

Kauai in May: 97% of days see measurable rain, 71°F average high, 0% of days historically clear (n=248, ERA5 2018–2025).

Kauai in May is historically a poor month for sun: only 0% of days clear across 8 years (n=248, avg high 71°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 May

Clear-sky percentage for Kauai in May, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early May
1st–15th		 0% n=120 71°F
Late May
16th–end		 0% n=128 71°F
Full month average 0% n=248 71°F

Sunshine & warmth in May

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 May. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early May
1st–15th		 22% n=120
Late May
16th–end		 44% n=128
Full month average 33% n=248
12.4 h median sunshine per day 91% of days exceed 8 h sunshine 97% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 0%. Sunshine-based “warm & sunny”: 33%. The 33-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 May: only 0% 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 ← this page 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 4% n=248 All destinations →

Frequently asked

Does it rain in Kauai in May?

Yes, frequently. In Kauai, 97% of days in May 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 May?

Not usually. Kauai is historically overcast in May: only 0% of days are clear (avg high 71°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.