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SunnyDays

ERA5 almanac — 8 years of real data

St. Martin in December

St. Martin in December: 39% of days see measurable rain, 77°F average high, 15% of days historically clear (n=248, ERA5 2018–2025).

St. Martin in December is historically a poor month for sun: only 15% of days clear across 8 years (n=248, avg high 77°F). March is the clearest month for St. Martin 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. Martin 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 St. Martin 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		 10% n=120 77°F
Late December
16th–end		 20% n=128 77°F
Full month average 15% n=248 77°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 St. Martin 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		 100% n=120
Late December
16th–end		 100% n=128
Full month average 100% n=248
10.5 h median sunshine per day 99% of days exceed 8 h sunshine 39% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 15%. Sunshine-based “warm & sunny”: 100%. The 85-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. Martin is a poor choice for sun in December: just 15% of days clear historically (n=248). March 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 March — historically the best month for sun in St. Martin.

Every month in St. Martin

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

Historical clear-sky % for St. Martin, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 18% n=248 All destinations →
February 11% n=226 All destinations →
March 28% n=248 All destinations →
April 24% n=240 All destinations →
May 24% n=248 All destinations →
June 18% n=240 All destinations →
July 11% n=248 All destinations →
August 16% n=248 All destinations →
September 15% n=240 All destinations →
October 18% n=248 All destinations →
November 17% n=240 All destinations →
December ← this page 15% n=248 All destinations →

Frequently asked

Does it rain in St. Martin in December?

Sometimes. St. Martin sees measurable rain on 39% of days in December historically (n=248 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is St. Martin good for sun in December?

Not usually. St. Martin is historically overcast in December: only 15% of days are clear (avg high 77°F, n=248 days, ERA5 2018–2025). March is historically far better for sun here.

How St. Martin compares in December

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