Thailand
Best Time to Dive in the Similan Islands
8.66°N 97.63°E
Closed June to September. Dive it December to April, when the downpours ease — 2 days a month of heavy rain instead of 9. Too few records to show a wildlife season, so the weather picks the month.
- Best time
- Dec–Apr
- Water
- 29–30 °C
- Visibility
- 20–30 m
- Dived from
- liveaboard
- Tidal range
- 0.9–2.1 m
- Species logged
- 4
Where it is
222 km across · coastline from Natural Earth 10m
Diving in the Similan Islands — monthly breakdown
A year of scuba diving conditions at a glance. Hover a month to isolate it.
| January | February | March | April | May | June | July | August | September | October | November | December | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Conditions | Excellent | Excellent | Excellent | Excellent | Poor | Poor | Poor | Poor | Poor | Poor | Excellent | Excellent |
| Water temp (°C) | 29 | 29 | 30 | 30 | 30 | 30 | 29 | 29 | 29 | 29 | 29 | 29 |
| Visibility (m) | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 |
| Marine life | Peak | Peak | Peak | Busy | Steady | Closed | Closed | Closed | Closed | Steady | Busy | Busy |
| Best time | Peak | Peak | Peak | Peak | Peak |
Excellent Good Moderate PoorPeak season Dec–Apr
Long-term averages, 2016–2025. Visibility is estimated from satellite chlorophyll-a. Water temperature is the surface mean; it is cooler at depth.
The Similan Islands diving season
May to October · Off season
6 monthsJFMAMJJASOND
- Water temperature
- 29–30 °C
- Visibility
- 20–30 m
- Rain
- 24 days a month
Diving conditionsThis is the wet season topside. The sea is rougher. The wind is up.
November to April · Peak season
6 monthsJFMAMJJASOND
- Water temperature
- 29–30 °C
- Visibility
- 20–30 m
- Rain
- 13 days a month
Diving conditionsRain is frequent topside. The sea is calmer. The wind eases.
Marine lifeOceanic manta (likely), Whale shark (likely) peak at Similan Islands in these months.
- Spring tides run 2.1 m against 0.9 m on neaps, so currents build around the full and new moon.
- Water temperature is satellite sea-surface temperature, so expect it cooler below the thermocline.
- Visibility is estimated from satellite chlorophyll-a.
Similan Islands water temperature and weather
110 underwater observation records · 22 surveyed years of ocean data · 10 years of sea temperature
Water & weather
Similan Islands water temperature by month
The dashed line is the monthly average. Eight days in ten fall inside the band.
10th to 90th percentile rangemonthly mean
Rarely
rough enough to cancel
Seas top 2.5 m on 1% of days. Enough to cancel a liveaboard crossing
1
blowy days a month
Gusts over 40 km/h, about where a day boat stays in port
19
wet days a month
6 of them bring heavy rain
| Month | Swell | Gusts over 40 km/h | Wet days | Heavy rain | Air | Daylight |
|---|---|---|---|---|---|---|
| January | 0.9 m | 0% | 10 | 1 | 28 °C | 11.5 h |
| February | 0.9 m | 0% | 7 | 1 | 29 °C | 11.7 h |
| March | 0.8 m | 0% | 9 | 1 | 29 °C | 11.9 h |
| April | 0.9 m | 0% | 17 | 3 | 30 °C | 12.2 h |
| May | 1.8 m | 2% | 26 | 10 | 30 °C | 12.4 h |
| June | 2.0 m | 3% | 23 | 8 | 29 °C | 12.5 h |
| July | 2.4 m | 10% | 22 | 8 | 29 °C | 12.5 h |
| August | 2.0 m | 7% | 23 | 9 | 29 °C | 12.3 h |
| September | 2.2 m | 6% | 24 | 11 | 28 °C | 12.0 h |
| October | 1.6 m | 1% | 27 | 11 | 28 °C | 11.8 h |
| November | 1.1 m | 0% | 23 | 7 | 29 °C | 11.6 h |
| December | 1.1 m | 0% | 14 | 2 | 28 °C | 11.5 h |
Swell is the rough end of the month: nine days in ten come in under it. Sea temperature covers 10 years, waves 4.
Pick your week
48 weeks from the daily record. Darker is better, against this site's own year. Pick a month for the detail.
| Week 1 | January week 1: Excellent | February week 1: Excellent | March week 1: Excellent | April week 1: Excellent | May week 1: Moderate | June week 1: Poor | July week 1: Poor | August week 1: Poor | September week 1: Poor | October week 1: Poor | November week 1: Excellent | December week 1: Excellent |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Week 2 | January week 2: Excellent | February week 2: Excellent | March week 2: Excellent | April week 2: Excellent | May week 2: Moderate | June week 2: Poor | July week 2: Poor | August week 2: Poor | September week 2: Poor | October week 2: Poor | November week 2: Excellent | December week 2: Excellent |
| Week 3 | January week 3: Excellent | February week 3: Excellent | March week 3: Excellent | April week 3: Excellent | May week 3: Poor | June week 3: Poor | July week 3: Poor | August week 3: Poor | September week 3: Poor | October week 3: Poor | November week 3: Excellent | December week 3: Excellent |
| Week 4 | January week 4: Excellent | February week 4: Excellent | March week 4: Excellent | April week 4: Excellent | May week 4: Poor | June week 4: Poor | July week 4: Poor | August week 4: Poor | September week 4: Poor | October week 4: Poor | November week 4: Excellent | December week 4: Excellent |
Excellent Good Moderate PoorBest week to go: first of March
January, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 29 °C | 0.9 m | 24 km/h | 30% |
| Week 2 | Excellent | 29 °C | 0.9 m | 22 km/h | 32% |
| Week 3 | Excellent | 29 °C | 0.9 m | 22 km/h | 34% |
| Week 4 | Excellent | 29 °C | 0.9 m | 21 km/h | 30% |
February, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 29 °C | 0.9 m | 21 km/h | 22% |
| Week 2 | Excellent | 29 °C | 0.9 m | 22 km/h | 20% |
| Week 3 | Excellent | 29 °C | 0.9 m | 21 km/h | 24% |
| Week 4 | Excellent | 29 °C | 0.9 m | 20 km/h | 24% |
March, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 29 °C | 0.9 m | 20 km/h | 19% |
| Week 2 | Excellent | 29 °C | 0.8 m | 19 km/h | 20% |
| Week 3 | Excellent | 30 °C | 0.9 m | 19 km/h | 29% |
| Week 4 | Excellent | 30 °C | 0.8 m | 19 km/h | 47% |
April, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 30 °C | 0.8 m | 18 km/h | 54% |
| Week 2 | Excellent | 30 °C | 0.9 m | 18 km/h | 50% |
| Week 3 | Excellent | 30 °C | 0.9 m | 18 km/h | 53% |
| Week 4 | Excellent | 31 °C | 0.8 m | 17 km/h | 67% |
May, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Moderate | 31 °C | 1.2 m | 17 km/h | 80% |
| Week 2 | Moderate | 30 °C | 1.5 m | 19 km/h | 85% |
| Week 3 | Poor | 30 °C | 1.8 m | 24 km/h | 86% |
| Week 4 | Poor | 30 °C | 2.0 m | 26 km/h | 82% |
June, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 30 °C | 2.1 m | 27 km/h | 79% |
| Week 2 | Poor | 30 °C | 2.0 m | 27 km/h | 72% |
| Week 3 | Poor | 30 °C | 2.0 m | 27 km/h | 72% |
| Week 4 | Poor | 29 °C | 2.0 m | 26 km/h | 72% |
July, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 30 °C | 2.2 m | 27 km/h | 70% |
| Week 2 | Poor | 29 °C | 2.5 m | 29 km/h | 76% |
| Week 3 | Poor | 29 °C | 2.5 m | 31 km/h | 69% |
| Week 4 | Poor | 29 °C | 2.2 m | 32 km/h | 68% |
August, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 29 °C | 2.1 m | 32 km/h | 74% |
| Week 2 | Poor | 29 °C | 1.9 m | 31 km/h | 73% |
| Week 3 | Poor | 29 °C | 1.8 m | 28 km/h | 69% |
| Week 4 | Poor | 29 °C | 2.0 m | 27 km/h | 76% |
September, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 29 °C | 2.2 m | 27 km/h | 79% |
| Week 2 | Poor | 29 °C | 2.2 m | 27 km/h | 81% |
| Week 3 | Poor | 29 °C | 2.0 m | 27 km/h | 81% |
| Week 4 | Poor | 29 °C | 2.1 m | 25 km/h | 80% |
October, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 29 °C | 1.8 m | 21 km/h | 84% |
| Week 2 | Poor | 29 °C | 1.4 m | 21 km/h | 89% |
| Week 3 | Poor | 29 °C | 1.8 m | 21 km/h | 90% |
| Week 4 | Poor | 29 °C | 1.6 m | 19 km/h | 87% |
November, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 29 °C | 1.4 m | 19 km/h | 85% |
| Week 2 | Excellent | 29 °C | 1.1 m | 18 km/h | 82% |
| Week 3 | Excellent | 29 °C | 1.0 m | 19 km/h | 77% |
| Week 4 | Excellent | 29 °C | 1.1 m | 23 km/h | 71% |
December, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 29 °C | 1.0 m | 23 km/h | 62% |
| Week 2 | Excellent | 29 °C | 1.1 m | 22 km/h | 54% |
| Week 3 | Excellent | 29 °C | 1.2 m | 23 km/h | 40% |
| Week 4 | Excellent | 29 °C | 1.1 m | 24 km/h | 27% |
10 years of daily records, averaged into weeks.
Gear & storms
What to wear
Off the coldest water of each month, not the average — that is what the suit has to cope with.
| January | February | March | April | May | June | July | August | September | October | November | December | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Suit | January: skin | February: skin | March: skin | April: skin | May: skin | June: skin | July: skin | August: skin | September: skin | October: skin | November: skin | December: skin |
One suit covers the whole year: a skin or 3 mm shorty.
Swell through the year
The rough end of each month — nine days in ten come in under it.
Amber is over 2.5 m.
Tides
Tropical storms
1 of the last 30 Januarys saw a tropical storm pass within 250 km. Anything has been recorded Jan, Nov.
Share of the last 30 years with a storm that month.
- NOAASea surface temperature, from OISST and MUR
- ERA5Wind, waves, rain and air temperature, via Open-Meteo
- OBISMarine species records within 60 km
- IBTrACSTropical cyclone tracks, 1996 to 2025
Similan Islands marine life — what you'll see diving
Only 110 records have been logged within 60 km. A thin record is not an empty reef.
| Species | When | Observed window | Reliability | Evidence | Records |
|---|---|---|---|---|---|
| Green turtle | Aug–Sep, Nov | Likely | 27 | ||
| Oceanic manta | Feb–Mar | Likely | 21 | ||
| Whale shark | Jan, Mar–Apr | Likely | 16 | ||
| Hawksbill turtle | Jan–Feb, May, Nov | Likely | 15 |
Peak Present No survey data
- Observed window
- Months with records. Peak is where most of them fall.
- Reliability
- Near-guaranteed in 60% of surveyed years or more
- Likely 30% to 60%
- Hit-or-miss under 30%
- Evidence
- Years it was seen, out of the years anyone surveyed.
- Records
- OBIS sightings within 60 km.
These are sightings people logged, not a full survey of the reef. A species missing from a month may just mean nobody recorded one.
Diving the Similan Islands — common questions
- When is the best time to dive the Similan Islands?
- Closed June to September. Dive it December to April, when the downpours ease — 2 days a month of heavy rain instead of 9. Too few records to show a wildlife season, so the weather picks the month.
- When is the diving season at the Similan Islands?
- The diving season at the Similan Islands runs December to April.
- Is the diving at the Similan Islands good for beginners?
- It is better with some experience. It suits Advanced Open Water divers or equivalent, so newer divers should ask the local operator which sites fit their level.
- How warm is the water at the Similan Islands?
- Between 29 and 30 °C at the surface across the year, coldest in January and warmest in May. It runs cooler below the thermocline.
- What wetsuit do I need at the Similan Islands?
- A skin or 3 mm shorty covers the coldest water of the year. The same suit works all year.
- What is the visibility like at the Similan Islands?
- Roughly 20 to 30 m depending on the month. That is estimated from satellite chlorophyll-a rather than measured in the water.
- What will I see diving the Similan Islands?
- The most consistently recorded species are Green turtle (likely), Oceanic manta (likely) and Whale shark (likely), from 110 records within 60 km.
- Does the Similan Islands get tropical storms?
- Yes. Over 30 years of records a storm passed within 250 km in Jan, Nov, most often in January at 1 of 30 years.
- Is there current at the Similan Islands?
- The tide rises and falls 2.1 m around the full and new moon, against 0.9 m in between. How much of that becomes current depends on the shape of the channel.
- When should I avoid the Similan Islands?
- The site is closed Jun–Sep. May–October are the weakest months for conditions.
- How do you dive the Similan Islands?
- Mostly from liveaboards. Trips run through the season, Dec–Apr.