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!).
Interesting Comparisons that may surprise you: