Skip to main content
SunnyDays

ERA5 almanac — 8 years of real data

Tulum in December

Tulum in December: 49% of days see measurable rain, 81°F average high, 21% of days historically clear (n=248, ERA5 2018–2025).

Tulum in December is historically a poor month for sun: only 21% of days clear across 8 years (n=248, avg high 81°F). April is the clearest month for Tulum 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 Tulum 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 Tulum 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		 21% n=120 81°F
Late December
16th–end		 21% n=128 81°F
Full month average 21% n=248 81°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 Tulum 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		 97% n=120
Late December
16th–end		 95% n=128
Full month average 96% n=248
10.3 h median sunshine per day 89% of days exceed 8 h sunshine 49% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 21%. Sunshine-based “warm & sunny”: 96%. The 75-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

Tulum is mostly overcast in December historically: only 21% of days are clear across 8 years (n=248), avg high 81°F. If you want sun in Tulum, 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 Tulum.

Every month in Tulum

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

Historical clear-sky % for Tulum, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 23% n=248 All destinations →
February 23% n=226 All destinations →
March 28% n=248 All destinations →
April 30% n=240 All destinations →
May 16% n=248 All destinations →
June 6% n=240 All destinations →
July 11% n=248 All destinations →
August 8% n=248 All destinations →
September 4% n=240 All destinations →
October 11% n=248 All destinations →
November 20% n=240 All destinations →
December ← this page 21% n=248 All destinations →

Frequently asked

Does it rain in Tulum in December?

Sometimes. Tulum sees measurable rain on 49% of days in December historically (n=248 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Tulum good for sun in December?

Not usually. Tulum is historically overcast in December: only 21% of days are clear (avg high 81°F, n=248 days, ERA5 2018–2025). April is historically far better for sun here.

How Tulum compares in December

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