TTDI Best-Months Heat Map — methodology
Ranked from measured data refreshed on a fixed cadence; the scoring thresholds are methodology choices, disclosed below.
The bands
Each month is classified from the city's monthly climate normals — average daily high, rainfall volume, rain days, and humidity. Ideal: 18–29 °C high, at most 90 mm of rain over at most 13 rain days, and not muggy-hot (27 °C or more combined with 75% humidity or more). Good: 13–33 °C, at most 130 mm over at most 16 rain days, and not muggy-hot (30 °C with 80% humidity). Difficult: below 5 °C, above 37 °C, 20+ rain days, or 200+ mm of rain — checked before Good, so a monsoon month with mild temperatures is named the problem it is. Everything else is Mixed: a real trade-off month, neither endorsed nor warned against.
Where the thresholds come from
The comfort ranges descend from the tourism-climatology literature — Mieczkowski's Tourism Climate Index (1985) and its successors place peak sightseeing comfort near 20–27 °C with low precipitation. Humidity disqualifies a month only in combination with heat, because mugginess is a heat-humidity interaction (the effective-temperature reasoning of that literature), and wetness is measured by rainfall volume alongside rain-day counts, because a drizzle-day is not a monsoon-day. Methodology v1.1 (2026-06-10) recalibrated the v1.0 thresholds against the covered cities' climate normals before first publication outreach; the change history is part of this disclosure. All thresholds are methodology choices, disclosed here and applied identically to every city.
The ranking
Cities are ranked by their count of Ideal months, most first. Equal counts share a rank; good-month counts are shown as context but never break ties — that would fabricate separation on a secondary metric.
The universe
Each edition ranks every city TTDI covered at the moment the edition was cut — the cities whose pages we publish and stand behind. The universe size is stated on every edition; an edition is never cut over fewer than 12 qualifying cities. As coverage grows, later editions rank more cities.
How ranks are assigned
Ranks are competition-style: cities with equal values share a rank, and the next distinct value resumes at its ordinal position (1, 2, 2, 4). We never separate tied cities alphabetically — a tie is reported as a tie.
Editions are frozen
Every edition is a frozen snapshot: once published, its ranking never changes, so a citation of this edition stays accurate. Updates ship as new editions at their own URLs; prior years remain available.