Tanzania
Best Time to Dive in Mafia Island
7.95°S 39.86°E
Go November to March for the calmest water — seas top 1.5 m on 3% of days, against 36% the rest of the year. Too few records to show a wildlife season, so the weather picks the month. The full season runs August to March.
- Best time
- Nov–Mar
- Water
- 26–30 °C
- Visibility
- 20–35 m
- Season runs
- Aug–Mar
- Dived from
- day boat
- Tidal range
- 1.4–3.5 m
- Species logged
- 1
Where it is
111 km across · coastline from Natural Earth 10m
Diving in Mafia 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 | Excellent | Excellent | Good | Poor | Poor | Poor | Poor | Moderate | Excellent | Excellent | Excellent | Excellent |
| Water temp (°C) | 29 | 29 | 30 | 29 | 28 | 27 | 26 | 26 | 26 | 27 | 28 | 29 |
| Visibility (m) | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 20–30 | 25–35 | 25–35 |
| Marine life | Peak | Peak | Quiet | Quiet | Quiet | Quiet | Quiet | Quiet | Busy | Peak | Busy | Busy |
| Best time | Peak | Peak | Peak | Peak | Peak |
Excellent Good Moderate PoorPeak season Nov–Mar
Long-term averages, 2016–2025. Visibility is estimated from satellite chlorophyll-a. Water temperature is the surface mean; it is cooler at depth.
The Mafia Island diving season
April to July · Off season
4 monthsJFMAMJJASOND
- Water temperature
- 26–29 °C
- Visibility
- 20–30 m
- Rain
- 17 days a month
Diving conditionsSwell is common, and crossings can be rough. The wind is up. It rains more.
August · Shoulder season
1 monthJFMAMJJASOND
- Water temperature
- 26–26 °C
- Visibility
- 20–30 m
- Rain
- 7 days a month
Diving conditionsThe sea is rougher. It rains less.
September to March · Peak season
7 monthsJFMAMJJASOND
- Water temperature
- 26–30 °C
- Visibility
- 20–30 m
- Rain
- 11 days a month
Diving conditionsThe wind eases. The sea is calmer.
Marine lifeWhale shark (near-guaranteed) peaks at Mafia Island in these months.
- Spring tides run 3.5 m against 1.4 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.
Mafia Island water temperature and weather
79 underwater observation records · 19 surveyed years of ocean data · 10 years of sea temperature
Water & weather
Mafia 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
7
rough days a month
Seas top 1.5 m on 22% of days. Enough to cancel a day boat
3
blowy days a month
Gusts over 40 km/h, about where a day boat stays in port
12
wet days a month
3 of them bring heavy rain
| Month | Swell | Gusts over 40 km/h | Wet days | Heavy rain | Air | Daylight |
|---|---|---|---|---|---|---|
| January | 1.4 m | 1% | 11 | 4 | 29 °C | 12.4 h |
| February | 1.3 m | 0% | 9 | 2 | 29 °C | 12.3 h |
| March | 1.1 m | 0% | 17 | 5 | 29 °C | 12.1 h |
| April | 1.7 m | 8% | 27 | 16 | 28 °C | 11.8 h |
| May | 1.9 m | 20% | 19 | 6 | 28 °C | 11.6 h |
| June | 2.0 m | 34% | 13 | 2 | 27 °C | 11.5 h |
| July | 1.9 m | 30% | 9 | 0 | 26 °C | 11.6 h |
| August | 1.8 m | 11% | 7 | 0 | 25 °C | 11.7 h |
| September | 1.6 m | 4% | 5 | 0 | 26 °C | 12.0 h |
| October | 1.6 m | 2% | 7 | 2 | 26 °C | 12.2 h |
| November | 1.4 m | 0% | 10 | 2 | 28 °C | 12.4 h |
| December | 1.1 m | 0% | 15 | 3 | 28 °C | 12.5 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: Good | February week 1: Excellent | March week 1: Good | April week 1: Poor | May week 1: Poor | June week 1: Poor | July week 1: Poor | August week 1: Poor | September week 1: Good | October week 1: Excellent | November week 1: Excellent | December week 1: Excellent |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Week 2 | January week 2: Excellent | February week 2: Excellent | March week 2: Good | April week 2: Poor | May week 2: Poor | June week 2: Poor | July week 2: Poor | August week 2: Moderate | September week 2: Good | October week 2: Excellent | November week 2: Excellent | December week 2: Excellent |
| Week 3 | January week 3: Good | February week 3: Excellent | March week 3: Excellent | April week 3: Poor | May week 3: Poor | June week 3: Poor | July week 3: Poor | August week 3: Good | September week 3: Excellent | October week 3: Excellent | 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: Poor | May week 4: Poor | June week 4: Poor | July week 4: Moderate | August week 4: Moderate | September week 4: Excellent | October week 4: Excellent | November week 4: Excellent | December week 4: Excellent |
Excellent Good Moderate PoorBest week to go: second of November
January, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Good | 29 °C | 1.2 m | 25 km/h | 40% |
| Week 2 | Excellent | 29 °C | 1.3 m | 26 km/h | 36% |
| Week 3 | Good | 29 °C | 1.5 m | 27 km/h | 36% |
| Week 4 | Excellent | 29 °C | 1.5 m | 26 km/h | 34% |
February, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 29 °C | 1.3 m | 25 km/h | 32% |
| Week 2 | Excellent | 29 °C | 1.2 m | 25 km/h | 29% |
| Week 3 | Excellent | 29 °C | 1.2 m | 23 km/h | 32% |
| Week 4 | Excellent | 29 °C | 1.3 m | 22 km/h | 36% |
March, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Good | 30 °C | 1.2 m | 22 km/h | 41% |
| Week 2 | Good | 30 °C | 1.2 m | 22 km/h | 44% |
| Week 3 | Excellent | 30 °C | 1.0 m | 21 km/h | 57% |
| Week 4 | Excellent | 30 °C | 1.0 m | 21 km/h | 76% |
April, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 30 °C | 1.1 m | 24 km/h | 85% |
| Week 2 | Poor | 29 °C | 1.5 m | 27 km/h | 91% |
| Week 3 | Poor | 29 °C | 1.7 m | 30 km/h | 92% |
| Week 4 | Poor | 29 °C | 1.9 m | 31 km/h | 86% |
May, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 29 °C | 2.0 m | 34 km/h | 80% |
| Week 2 | Poor | 28 °C | 1.9 m | 34 km/h | 68% |
| Week 3 | Poor | 28 °C | 1.9 m | 34 km/h | 56% |
| Week 4 | Poor | 28 °C | 1.9 m | 35 km/h | 50% |
June, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 28 °C | 1.9 m | 36 km/h | 46% |
| Week 2 | Poor | 28 °C | 2.0 m | 37 km/h | 40% |
| Week 3 | Poor | 27 °C | 2.0 m | 38 km/h | 42% |
| Week 4 | Poor | 27 °C | 2.0 m | 38 km/h | 46% |
July, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 27 °C | 2.0 m | 37 km/h | 40% |
| Week 2 | Poor | 26 °C | 2.0 m | 37 km/h | 35% |
| Week 3 | Poor | 26 °C | 1.9 m | 38 km/h | 29% |
| Week 4 | Moderate | 26 °C | 1.9 m | 36 km/h | 24% |
August, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 26 °C | 2.0 m | 33 km/h | 24% |
| Week 2 | Moderate | 26 °C | 1.7 m | 30 km/h | 21% |
| Week 3 | Good | 26 °C | 1.8 m | 29 km/h | 20% |
| Week 4 | Moderate | 26 °C | 1.8 m | 29 km/h | 19% |
September, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Good | 26 °C | 1.8 m | 29 km/h | 17% |
| Week 2 | Good | 26 °C | 1.6 m | 27 km/h | 14% |
| Week 3 | Excellent | 26 °C | 1.5 m | 27 km/h | 13% |
| Week 4 | Excellent | 26 °C | 1.6 m | 27 km/h | 18% |
October, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 26 °C | 1.7 m | 26 km/h | 20% |
| Week 2 | Excellent | 27 °C | 1.6 m | 26 km/h | 19% |
| Week 3 | Excellent | 27 °C | 1.4 m | 25 km/h | 20% |
| Week 4 | Excellent | 27 °C | 1.5 m | 25 km/h | 26% |
November, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 28 °C | 1.5 m | 25 km/h | 31% |
| Week 2 | Excellent | 28 °C | 1.3 m | 24 km/h | 29% |
| Week 3 | Excellent | 28 °C | 1.4 m | 23 km/h | 31% |
| Week 4 | Excellent | 28 °C | 1.5 m | 22 km/h | 38% |
December, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 29 °C | 1.1 m | 21 km/h | 46% |
| Week 2 | Excellent | 29 °C | 1.0 m | 21 km/h | 51% |
| Week 3 | Excellent | 29 °C | 1.1 m | 22 km/h | 47% |
| Week 4 | Excellent | 29 °C | 1.1 m | 24 km/h | 43% |
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: 3 mm | July: 3 mm | August: 3 mm | September: 3 mm | October: 3 mm | November: skin | December: skin |
- Nov–Mayskin or 3 mm shorty
- Jun–Oct3 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
1 of the last 30 Aprils saw a tropical storm pass within 250 km. Anything has been recorded Apr–May.
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
Mafia Island marine life — what you'll see diving
Only 79 records have been logged within 60 km. A thin record is not an empty reef.
| Species | When | Observed window | Reliability | Evidence | Records |
|---|---|---|---|---|---|
| Whale shark | Jan–Feb, Oct | Near-guaranteed | 46 |
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 Mafia Island — common questions
- When is the best time to dive Mafia Island?
- Go November to March for the calmest water — seas top 1.5 m on 3% of days, against 36% the rest of the year. Too few records to show a wildlife season, so the weather picks the month. The full season runs August to March.
- When is the diving season in Mafia Island?
- The diving season in Mafia Island runs August to March, and it is at its best November to March.
- Is the diving in Mafia Island good for beginners?
- Yes. It is known as a snorkelling site as much as a dive site, so no experience is needed to get in the water.
- How warm is the water in Mafia Island?
- Between 26 and 30 °C at the surface across the year, coldest in August and warmest in March. It runs cooler below the thermocline.
- What wetsuit do I need in Mafia Island?
- A 3 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 Mafia 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 Mafia Island?
- The most consistently recorded species are Whale shark (near-guaranteed), from 79 records within 60 km.
- Does Mafia Island get tropical storms?
- Yes. Over 30 years of records a storm passed within 250 km in Apr–May, most often in April at 1 of 30 years.
- Is there current in Mafia Island?
- The tide rises and falls 3.5 m around the full and new moon, against 1.4 m in between. How much of that becomes current depends on the shape of the channel.
- When should I avoid Mafia Island?
- April–May are the weakest months for conditions.
- How do you dive Mafia Island?
- Mostly from day boats. Trips run through the season, Aug–Mar.