The archipelago is spread out in the area between 37° N and the parallels of latitude that pass through the Lisbon area (39° 43' / 39° 55' N), giving it a tepid, oceanic, subtropical climate, with mild annual oscillations.
The average annual rainfall increases from east to west, and it ranges from 700 to 1600 annual millimetres (27.6–63 in) on average, reaching 6,300 millimetres (250 in) on Mount Pico, the highest Portuguese mountain at 2,351 m/7,713 ft. The Azores high, an area of high atmospheric pressure, is named after the islands.
The Formigas (the Portuguese word for "ants") islands (also known as Dollabarat Reefs) have rich maritime fauna, including exotic species such as the black coral and manta rays, sharks, and sea turtles.
The archipelago lies in the Palearctic ecozone, forming a unique biome that includes the macaronesian subtropical laurissilva, with many endemic species of plants.
Even though the Azores look very green and sometimes wild, the vegetation has been extremely altered. Most of the original laurisilva has been wiped out for its valuable wood (for tools, buildings, boats, fire wood, etc) and to clear land for agriculture.
Many cultivated places (which are traditionally dedicated to pasture or to growing colocasia, potatoes, maize and other crops) have now been abandoned, especially as a result of emigration.
Consequently, some invasive plants have filled these deserted and disturbed lands. The two most common of these exotic species are Pittosporum undulatum and Acacia melanoxylon. They are usually restricted to ancient agricultural land and, fortunately, only rarely penetrate into undisturbed native vegetation. The main loss is in the lowlands (below 400 metres), where virtually all laurisilva was eradicated.
A few Persea indica and Picconia azorica still survive in some places, but appear to be extremely vulnerable. Only Myrica faya seems to have survived human impact quite well, and it is commonly found in hedges or among exotic trees. More recent introductions could become a serious threat, like Leptospermum scoparium which has the ability to colonize the still nearly-untouched medium-altitude vegetation (Ilex, Myrsine africana, Erica, etc).
Hydrangeas are another potential pest, but their threat is less serious. Notwithstanding the fact that Hydrangeas were introduced from America or Asia, some locals consider them to be a symbol of the archipelago and propagate them along roadsides, helping them to escape into the wild. Cryptomeria, the Japanese cedar, is a conifer extensively grown for its timber; many seedlings can be found in the last remnants of medium-altitude native vegetation.
The Azores only endemic bird species is the Azores Bullfinch, or Priolo, which is retricted to remnant laurisilva forest in the mountains at the eastern end of São Miguel. It is listed as critically endangered. The Azores also has an endemic bat, the Azores Noctule, which is unusual in regularly feeding during the day.
The nine islands have a total area of 2,346 km2 (906 sq mi). Their individual areas range between São Miguel's 759 km2 (293 sq mi) and Corvo's 17 km2 (7 sq mi). Three islands (São Miguel, Pico and Terceira) are larger than Malta (composed of three islands), São Miguel Island alone being twice as large.
The nine islands are divided into three groups:
* The Eastern Group (Grupo Oriental) of São Miguel, Santa Maria and Formigas Islets
* The Central Group (Grupo Central) of Terceira, Graciosa, São Jorge, Pico and Faial
* The Western Group (Grupo Ocidental) of Flores and Corvo.