Our method and data
Every month at every destination is rated from up to ten years of sea and weather records taken at the dive site itself, 30 years of storm tracks and 340,098 logged marine life sightings.
Across 6 regions, each pinned by hand
With enough data to compare against every other
Animals recorded at four or more destinations
Where the data comes from
| Source | What we take from it |
|---|---|
| NOAA OISST · NASA MUR | 10 years of daily sea temperature from satellites, 2016–2025 |
| ERA5 | 10 years of rain, wind and air temperature, via Open-Meteo |
| Open-Meteo Marine | 4 years of wave height, 2022–2025 |
| OBIS | 340,098 marine life records across 223 destinations |
| NOAA VIIRS | Satellite readings of plankton since 2012, used to estimate visibility |
| IBTrACS | 30 years of cyclone tracks; 153 of 235 destinations sit within 250 km of one |
| Open-Meteo | Delivers the ERA5 weather and wave records, and hourly sea level since 2023 for the tide range |
| Natural Earth | Coastlines for the maps, which are for finding a place, not for navigation |
Each destination is a pin on the water where the diving happens, not on the nearest town, and every reading is taken at that pin.
How a month is rated
1. Conditions
Six things decide whether the diving is pleasant and whether boats go out. Each is worked out for every month from daily records: ten years of sea temperature and weather, four of waves.
| Factor | Counts | What we look at |
|---|---|---|
| Waves | Most | How often the sea gets too rough for the way the site is dived |
| Wind | Most | How often it blows hard enough to chop up the surface or keep boats in |
| Heavy rain | A lot | Days of proper downpour, the kind that cancels boats and muddies the water |
| Water temperature | Some | Warmer is nicer, but cold water is a wetsuit question, so it never sinks a month on its own |
| Air temperature | Some | How pleasant it is on the boat and between dives |
| Daylight | Some | Enough light for a full day of diving |
What counts as rough depends on how you get in. A shore entry suffers from half a metre of wave, a day boat from a metre, and a liveaboard shrugs off anything under a metre and a half.
2. Storms
For each month we count how many of the last 30 years had a tropical storm, cyclone or hurricane pass within 250 km. That is the storm chance you see on every page, and the higher it is, the more the month is marked down.
3. Closures
Some parks and marine reserves close for part of the year. Where a closure is known, those months are marked closed and score nothing, however good the weather.
4. Wildlife
Each month also gets a wildlife score from the animals recorded near the site: how many of the headline animals are there, whether it is their peak, and how reliably they turn up from year to year. Where people travel for one animal, its season counts about as much as the weather.
5. The best time to go
The best time is the stretch of months closest to the site's own best, five at most, so even a good all-year site points you to its strongest run. Where the animals peak at a different time from the calm water, the page says so and names both.
6. Comparing places
"Good", "Moderate" and "Off season" on a destination page compare the site with itself. On the world map and in the month rankings, each month is placed in the top, middle or bottom third of all 149 rated destinations. To be rated worldwide a site needs a clear satellite view of its sea and at least 200 marine life records nearby; the rest still get a season, just not a world ranking.
Marine life
Sightings come from OBIS, the Ocean Biodiversity Information System, which collects records from scientific surveys, research trips and citizen science. We count every record within 60 km of a destination, and allow for how many people were looking each month, so a busy survey season does not pass for a migration.
| On the page | What it means |
|---|---|
| Peak season | The months when most sightings happen |
| Near-guaranteed | Seen in its season in at least 6 of every 10 years with records since 1995 |
| Likely | Seen in 3 to 6 of every 10 of those years |
| Hit-or-miss | Seen in fewer than 3 of every 10 |
| Few records | Fewer than 30 records, so the season is a guide rather than a promise |
An animal needs at least 8 records to appear at all. Records show where someone was looking: a month with no sightings may just mean nobody logged one.
Visibility, wetsuits and tides
Visibility is an estimate
Satellites can see the green of plankton in the water, and plankton is what clouds most tropical seas. From monthly readings since 2012, clear blue water with little plankton reads as 30 m or more, and green, plankton-rich water as under 10 m.
It cannot see river silt, sand stirred up by storms or a bright shallow bottom, and it is blind under cloud. Plankton is also what feeds mantas and whale sharks, so greener water can mean bigger animals. The estimate is shown on each page but does not change the rating.
Wetsuit guide
The suit is picked for the colder days of the month, not the average, so you are warm on the chilliest dive of the trip:
| Water on the colder days | Suit |
|---|---|
| 27 °C and above | Skin or 3 mm shorty |
| 24 °C and above | 3 mm full suit |
| 21 °C and above | 5 mm full suit |
| 17 °C and above | 5 mm with hood and gloves |
| 13 °C and above | 7 mm semi-dry |
| Below 13 °C | Drysuit |
These are surface temperatures; expect cooler water below the thermocline.
Tides
The tide range comes from hourly sea level readings since 2023, and is shown where spring tides move the sea a metre and a half or more. It is the rise and fall, not the strength of the current.
What the ratings cannot tell you
- Currents. There is no reliable current data, so drifts and ripping channels are not rated.
- Coral health. Bleaching and reef damage change faster than any ten-year average.
- Operators. Boats, liveaboard schedules and prices are not modelled; a great month can still be one when few boats run.
- This year. Every figure is a long-run pattern. An El Niño year or a late monsoon will not follow it.
Method: common questions
- Where does besttimetodive.com get its data?
- From public science data: NOAA and NASA satellites for sea temperature and plankton, the ERA5 weather record, Open-Meteo Marine for waves and tides, NOAA's IBTrACS for storm tracks and OBIS for marine life sightings.
- Is the visibility figure measured?
- No. It is an estimate from satellite readings of plankton in the water. It cannot see silt from rivers or sand stirred up by storms, so treat it as a guide to how clear the water tends to be.
- Why does a destination say an animal is hit-or-miss when divers see it often?
- The ratings come from logged sightings. If few people have recorded an animal near a site, the record is thin and the rating stays cautious. A quiet month may just mean nobody logged a record.
- How often is the data updated?
- Sea temperature and weather cover 2016 to 2025, waves 2022 to 2025, storm tracks the last 30 full years and marine life every OBIS record near each site. Everything is computed from those sources, apart from a hand-checked list of park closures, sheltered bays and the animals each site is known for.