Taiwan
Best Time to Dive in Green Island
22.64°N 121.53°E
Plan for March to June for the calmest water — seas top 1.5 m on 53% of days, against 72% the rest of the year. Too few records to show a wildlife season, so the weather picks the month.
- Best time
- Mar–Jun
- Water
- 25–30 °C
- Visibility
- 20–35 m
- Dived from
- day boat
- Tidal range
- 0.8–1.7 m
- Species logged
- 2
Worth knowing: 92% of days see seas over 1.5 m.
Where it is
111 km across · coastline from Natural Earth 10m
Diving in Green Island — 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 | Poor | Moderate | Excellent | Excellent | Good | Good | Poor | Poor | Poor | Poor | Poor | Poor |
| Water temp (°C) | 25 | 25 | 25 | 27 | 28 | 29 | 30 | 29 | 29 | 28 | 27 | 26 |
| Visibility (m) | 20–30 | 25–35 | 25–35 | 25–35 | 25–35 | 25–35 | 25–35 | 25–35 | 25–35 | 25–35 | 20–30 | 20–30 |
| Marine life | Steady | Steady | Steady | Steady | Steady | Steady | Steady | Steady | Steady | Steady | Steady | Steady |
| Best time | Peak | Peak | Peak | Peak |
Excellent Good Moderate PoorPeak season Mar–Jun
Long-term averages, 2016–2025. Visibility is estimated from satellite chlorophyll-a. Water temperature is the surface mean; it is cooler at depth.
The Green Island diving season
February · Shoulder season
1 monthJFMAMJJASOND
- Water temperature
- 25–25 °C
- Visibility
- 25–35 m
- Rain
- 20 days a month
Diving conditionsThis is the wet season topside.
March to June · Peak season
4 monthsJFMAMJJASOND
- Water temperature
- 25–29 °C
- Visibility
- 25–35 m
- Rain
- 15 days a month
Diving conditionsIt rains less.
July to January · Off season
7 monthsJFMAMJJASOND
- Water temperature
- 25–30 °C
- Visibility
- 25–35 m
- Rain
- 19 days a month
Diving conditionsIt rains more.
- Spring tides run 1.7 m against 0.8 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.
Green Island water temperature and weather
84 underwater observation records · 16 surveyed years of ocean data · 10 years of sea temperature
Water & weather
Green Island 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
20
rough days a month
Seas top 1.5 m on 66% of days. Enough to cancel a day boat
12
blowy days a month
Gusts over 40 km/h, about where a day boat stays in port
18
wet days a month
4 of them bring heavy rain
| Month | Swell | Gusts over 40 km/h | Wet days | Heavy rain | Air | Daylight |
|---|---|---|---|---|---|---|
| January | 3.6 m | 55% | 24 | 5 | 22 °C | 10.8 h |
| February | 3.8 m | 52% | 20 | 3 | 22 °C | 11.2 h |
| March | 3.1 m | 38% | 16 | 2 | 24 °C | 11.8 h |
| April | 2.8 m | 31% | 14 | 1 | 26 °C | 12.5 h |
| May | 2.5 m | 27% | 16 | 4 | 28 °C | 13.1 h |
| June | 2.0 m | 34% | 13 | 4 | 29 °C | 13.4 h |
| July | 3.4 m | 28% | 13 | 4 | 30 °C | 13.3 h |
| August | 2.2 m | 19% | 15 | 5 | 29 °C | 12.8 h |
| September | 3.2 m | 18% | 18 | 5 | 29 °C | 12.1 h |
| October | 4.8 m | 48% | 21 | 7 | 27 °C | 11.5 h |
| November | 3.8 m | 52% | 21 | 5 | 26 °C | 10.9 h |
| December | 4.3 m | 69% | 24 | 6 | 23 °C | 10.6 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: Poor | February week 1: Moderate | March week 1: Good | April week 1: Good | May week 1: Excellent | June week 1: Moderate | July week 1: Poor | August week 1: Poor | September week 1: Poor | October week 1: Poor | November week 1: Poor | December week 1: Poor |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Week 2 | January week 2: Poor | February week 2: Moderate | March week 2: Good | April week 2: Excellent | May week 2: Excellent | June week 2: Moderate | July week 2: Moderate | August week 2: Moderate | September week 2: Poor | October week 2: Poor | November week 2: Poor | December week 2: Poor |
| Week 3 | January week 3: Poor | February week 3: Moderate | March week 3: Excellent | April week 3: Excellent | May week 3: Excellent | June week 3: Excellent | July week 3: Poor | August week 3: Moderate | September week 3: Poor | October week 3: Poor | November week 3: Poor | December week 3: Poor |
| Week 4 | January week 4: Poor | February week 4: Moderate | March week 4: Excellent | April week 4: Excellent | May week 4: Moderate | June week 4: Excellent | July week 4: Poor | August week 4: Poor | September week 4: Poor | October week 4: Poor | November week 4: Poor | December week 4: Poor |
Excellent Good Moderate PoorBest week to go: fourth of April
January, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 25 °C | 3.6 m | 44 km/h | 74% |
| Week 2 | Poor | 25 °C | 3.5 m | 42 km/h | 74% |
| Week 3 | Poor | 25 °C | 3.8 m | 42 km/h | 81% |
| Week 4 | Poor | 25 °C | 3.7 m | 41 km/h | 79% |
February, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Moderate | 25 °C | 3.5 m | 41 km/h | 74% |
| Week 2 | Moderate | 25 °C | 3.5 m | 40 km/h | 73% |
| Week 3 | Moderate | 25 °C | 3.8 m | 41 km/h | 69% |
| Week 4 | Moderate | 25 °C | 4.0 m | 40 km/h | 65% |
March, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Good | 25 °C | 3.5 m | 39 km/h | 61% |
| Week 2 | Good | 25 °C | 3.3 m | 37 km/h | 54% |
| Week 3 | Excellent | 26 °C | 2.8 m | 35 km/h | 49% |
| Week 4 | Excellent | 26 °C | 3.0 m | 36 km/h | 48% |
April, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Good | 26 °C | 3.2 m | 34 km/h | 47% |
| Week 2 | Excellent | 26 °C | 2.9 m | 34 km/h | 47% |
| Week 3 | Excellent | 27 °C | 2.5 m | 34 km/h | 45% |
| Week 4 | Excellent | 27 °C | 2.3 m | 34 km/h | 45% |
May, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 28 °C | 2.5 m | 33 km/h | 44% |
| Week 2 | Excellent | 28 °C | 2.5 m | 31 km/h | 49% |
| Week 3 | Excellent | 28 °C | 2.4 m | 30 km/h | 58% |
| Week 4 | Moderate | 29 °C | 2.9 m | 34 km/h | 51% |
June, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Moderate | 29 °C | 2.8 m | 33 km/h | 48% |
| Week 2 | Moderate | 29 °C | 2.2 m | 35 km/h | 47% |
| Week 3 | Excellent | 29 °C | 1.9 m | 35 km/h | 34% |
| Week 4 | Excellent | 29 °C | 1.6 m | 28 km/h | 39% |
July, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 30 °C | 2.0 m | 27 km/h | 47% |
| Week 2 | Moderate | 30 °C | 2.0 m | 27 km/h | 39% |
| Week 3 | Poor | 30 °C | 3.6 m | 25 km/h | 41% |
| Week 4 | Poor | 30 °C | 4.4 m | 25 km/h | 47% |
August, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 29 °C | 3.4 m | 25 km/h | 44% |
| Week 2 | Moderate | 29 °C | 2.1 m | 24 km/h | 42% |
| Week 3 | Moderate | 29 °C | 1.8 m | 24 km/h | 48% |
| Week 4 | Poor | 29 °C | 2.8 m | 24 km/h | 56% |
September, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 29 °C | 3.5 m | 25 km/h | 58% |
| Week 2 | Poor | 29 °C | 3.0 m | 25 km/h | 55% |
| Week 3 | Poor | 29 °C | 2.9 m | 27 km/h | 58% |
| Week 4 | Poor | 29 °C | 4.1 m | 32 km/h | 60% |
October, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 29 °C | 4.4 m | 34 km/h | 68% |
| Week 2 | Poor | 28 °C | 3.9 m | 38 km/h | 75% |
| Week 3 | Poor | 28 °C | 4.7 m | 42 km/h | 67% |
| Week 4 | Poor | 28 °C | 5.1 m | 45 km/h | 62% |
November, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 27 °C | 4.8 m | 45 km/h | 63% |
| Week 2 | Poor | 27 °C | 4.3 m | 39 km/h | 66% |
| Week 3 | Poor | 27 °C | 3.9 m | 39 km/h | 73% |
| Week 4 | Poor | 27 °C | 3.6 m | 44 km/h | 75% |
December, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 26 °C | 3.8 m | 47 km/h | 77% |
| Week 2 | Poor | 26 °C | 4.3 m | 47 km/h | 78% |
| Week 3 | Poor | 26 °C | 4.4 m | 47 km/h | 73% |
| Week 4 | Poor | 25 °C | 4.2 m | 47 km/h | 74% |
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: 5 mm | February: 3 mm | March: 3 mm | April: 3 mm | May: skin | June: skin | July: skin | August: skin | September: skin | October: skin | November: 3 mm | December: 3 mm |
- Jan5 mm full suit
- Feb–Apr3 mm full suit
- May–Octskin or 3 mm shorty
- Nov–Dec3 mm full suit
Swell through the year
The rough end of each month — nine days in ten come in under it.
Amber is over 1.5 m.
Tides
Tropical storms
19 of the last 30 Septembers saw a tropical storm pass within 250 km. Anything has been recorded Apr–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
Green Island marine life — what you'll see diving
Only 84 records have been logged within 60 km. A thin record is not an empty reef.
| Species | When | Observed window | Reliability | Evidence | Records |
|---|---|---|---|---|---|
| Green turtle | All year | Near-guaranteed | 46 | ||
| Loggerhead turtle | Feb | Hit-or-miss | 11 |
Peak Present
- 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 Green Island — common questions
- When is the best time to dive Green Island?
- Plan for March to June for the calmest water — seas top 1.5 m on 53% of days, against 72% the rest of the year. Too few records to show a wildlife season, so the weather picks the month.
- When is the diving season in Green Island?
- The diving season in Green Island runs March to June.
- Is the diving in Green Island good for beginners?
- Yes. It suits Open Water divers, so it works for a first trip after certification.
- How warm is the water in Green Island?
- Between 25 and 30 °C at the surface across the year, coldest in January and warmest in July. It runs cooler below the thermocline.
- What wetsuit do I need in Green Island?
- A 5 mm full suit covers the coldest water of the year. In the warmest months a skin or 3 mm shorty is enough.
- What is the visibility like in Green Island?
- Roughly 20 to 35 m depending on the month. That is estimated from satellite chlorophyll-a rather than measured in the water.
- What will I see diving Green Island?
- The most consistently recorded species are Green turtle (near-guaranteed) and Loggerhead turtle (hit-or-miss), from 84 records within 60 km.
- Does Green Island get tropical storms?
- Yes. Over 30 years of records a storm passed within 250 km in Apr–Nov, most often in September at 19 of 30 years.
- Is there current in Green Island?
- The tide rises and falls 1.7 m around the full and new moon, against 0.8 m in between. How much of that becomes current depends on the shape of the channel.
- When should I avoid Green Island?
- July, September–December are the weakest months for conditions.
- How do you dive Green Island?
- Mostly from day boats. Trips run through the season, Mar–Jun.