Tristan da Cunha's Climate
Tristan has a cool temperate oceanic climate, with an annual mean temperature of 15.1C, frequent gale force winds, persistent cloud and regular rainfall.

Tristan's Climate in a Nutshell

The Tristan da Cunha Settlement lies at 37 °S at the same latitude as Melbourne, Australia. So it is more influenced by tropical than polar air masses, is well north of the limit of drifting ice-bergs and is one of the most northerly locations for breeding penguins, commonly associated with the Antarctic environment.

Tristan has a cool temperate oceanic climate, with the Settlement experiencing no frosts although winter snow covers the Peak and can extend down to the Base. Summer temperatures rarely exceed 25 °C, with an annual mean of 15.1°C. Frequent storms bring gale force winds causing uplift of the moist air producing persistent cloud and regular rainfall in excess of 1500mm at sea level and over 3000mm of rain and snow on the mountain. High humidity can make drying and storing clothes problematic, especially as the prevailing north-west wind blows from the tropics and then the cloud base (100% humidity) may be below 500 metres.

As with many similar climates when anticyclonic conditions prevail there are light winds and clear sunny days, so, at this latitude days are warm even in winter. The cooling influence of the sea in summer (maximum 18 °C in February) prevents the high temperatures experienced at this latitude in Australia or in Southern Spain at the same latitude north of the Equator. Conversely sea temperatures drop to only 13 °C in winter, so have a warming effect. As a result Tristan is warmer in winter than Cape Town (see below).

 

Precipitation falls as snow on higher ground in winter months, often lying on the Peak for several months and can be seen on the high cliffs above the Patches, typically in July to September.

The Tristan mountain always creates a lee which typically has calm weather and sunshine even during a storm. So local climate around the island can vary a great deal. As a result Sandy Point, at the eastern extremity of Tristan is drier and warmer than the Settlement as it experiences a 'rain shadow' effect.

Nightingale Island reaches only 370 metres above sea level, so orographic uplift is far less than Tristan, so the island is generally drier and warmer.

Gough Island lies in the 'Roaring Forties' at latitude 40 °S and is cooler (annual mean 11.3 °C) and wetter (annual mean 3397mm = twice as wet as Tristan!).

July
Aug
Sept
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
June
Annual
Temperatures °C
Average Maximum
14
14
14
15
17
19
20
21
20
18
17
15
17
Average Mean
12.5
12
12
13
15
17
18
19
18
16.5
15
13
15.1
Average Minimum
11
10
10
11
13
15
16
17
16
15
13
11
13.2
Sea Temperature
14
13
13
14
15
16
17
18
18
17
16
15
15.5
                           
UV Index
2
3
5
7
10
11
11
10
8
5
3
2
6.4
Precipitation mm
160
175
169
151
128
127
93
113
121
129
155
160
1681
Number of wet days
25
26
24
22
18
19
18
16
17
20
23
23
251
Probability of rain per day %
81
84
80
71
61
61
58
57
55
67
74
77
69
Daylight Hours
Hours of Daylight
10
11
12
13
14
14.5
14
13
12
11
10
9.5
12
% sun
34
32
33
33
32
29
31
35
38
38
35
34
34
% cloud
66
68
67
67
68
71
69
65
62
62
65
66
66
Relative Humidity %
79
79
78
79
79
80
79
77
75
78
78
79
78.3
Comparison with UK, South Africa, Falklands and two islands with a similar latitude
Annual Figures
Tristan
Cape Town
London
Stanley, Falklands
Sao Miguel, Azores
Amsterdam Island Indian Ocean
Latitude (not rounded)
37
34
51
51
37
37
 
Temperatures °C
Average Maximum
17
22
14
9
20
16
Average Mean
15.1
17
10
6
17
13.8
Average Minimum
13.2
12
7
2
14
12
Sea Temperature Range
13 - 18
15 - 19
8 - 17 *
5 - 9
16 - 23
N / A
UV Index Range
2 - 11
3-11
0 - 6
0 - 8
2 - 9
N / A
Precipitation mm
1681
475
594
604
1026
1119
Number of wet days
251
101
164
133
188
N / A
Probability of rain per day %
69
28
45
36
52
N / A
             
Notes            
* Sea Temperatures for Brighton

Interesting Comparisons that may surprise you:
Tristan is warmer on average than Cape Town in winter
UV index is just as high in summer as in Cape Town and much higher than South-East England all the year round.
Tristan is much warmer than South-East England, especially in winter.