WhenToDive’s core claim is that dive trip planning should be a data problem. The ocean operates on predictable seasons, the animals follow the food, and the weather is boringly cyclic at most latitudes. Dive operators know this — every serious one can tell you the best month at their site and why. The problem is that there has never been a single place to compare that knowledge across destinations.
So WhenToDive’s first project was to build one. Twenty-eight destinations, scored month-by-month on a five-point scale, with water temperature, visibility, conditions, and rainfall tracked separately. The result powers the search tool, the destination comparison, and the individual destination pages.
With the full dataset in place, a few patterns jumped out. None of them are surprising to anyone who has dived professionally. What is surprising is how rarely they appear in dive travel writing, which mostly treats “best time to dive X” as a question answered destination by destination rather than a global calendar.
How the scoring works
Every destination is scored from 1 (genuinely bad) to 5 (excellent) for each of the twelve months of the year. The score is a holistic judgement of dive quality that rolls up visibility, sea conditions, species activity, and seasonal events like manta aggregations or shark peaks. It is deliberately simple — any ratings system that requires a legend to interpret is already a failure for a trip-planning tool.
Scores are built from dive operator season guides, liveaboard schedules, and published climate data. The goal is a single number you can trust at a glance without needing to decode it.
With all that in hand, here’s what the aggregated data shows.
Finding 1: March is the strongest dive month globally. September is the worst.
Summing the monthly scores across all 28 destinations produces a rough “global dive quality” index out of a possible 140. The months don’t come out evenly:
Out of 140 possible (28 destinations × 5-point scale). Browse all destinations →
Two patterns jump out:
- March is the single strongest month, with a cluster of four months close behind (April, May, January, February) all within six points of the leader. These are the windows where the widest range of world-class destinations are at or near peak: Tubbataha opens, Raja Ampat is in its calm dry season, the Red Sea is warming, the central Maldives dry window is in full swing, and Southeast Asia macro destinations are all running.
- August through October is the weakest band globally, bottoming out in September. The Asian typhoon season is active, the Caribbean hurricane season is at peak risk, and much of the Indo-Pacific is between monsoons. October is counter-intuitively second-worst despite being the start of Red Sea oceanic whitetip season — at aggregate scale, too many other destinations are in transition.
The planning implication is that travellers with flexibility on the destination but a fixed month have the widest range of options in the January-through-May window. October and September narrow the options significantly — though as Finding 5 shows, “narrower” is still not “nothing.”
Finding 2: Only eight destinations are genuinely diveable year-round
Of the 28 destinations in the dataset, eight score 4 or higher in ten or more months of the year. Six score 4+ in all twelve months:
Two more miss the cutoff by a single month each — La Paz dips in March and April as the Sea of Cortez transitions out of the whale shark and mobula aggregation window, and the Red Sea offshore reefs cool and roughen in January and February before the spring dive window opens:
Every other destination has a meaningful low season.
At the other extreme, some destinations have windows so narrow that missing them means missing the entire point of going:
This is the opposite of how most dive travel is marketed, which tends to imply that any destination is diveable year-round with some trade-off. For many destinations, the off-season isn’t a trade-off — it’s the destination actively being bad, closed, or inaccessible.
Finding 3: Species drive seasons more than weather does
Among the destinations that can dive year-round, the reason a particular month is flagged “peak” is almost always a species event rather than a weather event.
- Ningaloo’s March-to-August peak is whale sharks. The weather is fine year-round; the whale sharks are the reason the season exists.
- Galápagos’s June-to-November peak is hammerheads and whale sharks, triggered by the cold Humboldt current. The warm season is still plenty diveable; the peak season has the animals.
- Isla Mujeres’s December-to-March peak is sailfish and bulls; the summer window is whale sharks. Same destination, two different peak reasons, determined by species.
Whale sharks illustrate the point well. They are present somewhere in the world every month of the year, but their calendar is tied to specific locations with specific biology — not to global weather patterns:
Whale shark seasonality by destination. Dark = peak · mid = present · light = occasional sightings · empty = absent.
No single month is whale shark season everywhere. The right question isn’t “when is whale shark season” — it’s “which destination’s whale shark season fits my calendar.” Trip planning that ignores species timing is trip planning that optimizes for the wrong variable.
Finding 4: “Shoulder season” is a real phenomenon, not a hedge
Industry marketing tends to use “shoulder season” as polite phrasing for “the cheap bad time.” In the dataset, however, genuine shoulder windows produce legitimately excellent diving at lower prices. Examples:
- March in the Red Sea — water is warming, visibility is excellent, operators are not at peak capacity. Oceanic whitetips haven’t arrived yet (October) and hammerheads haven’t peaked at Daedalus (summer), but the offshore reefs are in outstanding shape.
- November in the Maldives — end of southwest monsoon, mantas still peaking, northeast monsoon visibility returning. Prices below January–March peak.
- November in Palau — post-rainy-season visibility, pelagic activity returning, still pre-December-rush.
A diver optimizing for dive quality per dollar of travel spend should be looking at these windows, not at the conventional peak-week-in-February default.
Finding 5: There is no month when nothing is worth diving
Even September — the worst month globally by aggregate score — has nine destinations scoring 5/5: Cocos Island (peak hammerhead season), Galápagos (whale shark window), Komodo (late dry season), La Paz (Sea of Cortez summer), Lembeh Strait (macro peak), the central Maldives (late southwest monsoon), Marsa Alam (Red Sea year-round reliability), Nusa Penida (mola still showing), and the Red Sea offshore reefs (just before the oceanic whitetip peak). The “bad globally” months are still world-class somewhere.
This is the core observation that made the WhenToDive dataset worth building. The world’s dive season is always peaking somewhere. A structured view across destinations makes that somewhere findable, rather than requiring the planner to already know it.
The data, browsable
Every destination’s month-by-month heatmap is on its individual page. The search tool takes any filter combination — month, species, region, skill, budget — and returns destinations ranked by the selected month’s score. The compare tool puts up to three destinations side by side to see exactly where their seasons align.