The prevailing weather conditions in the region of the Madeira Islands, found in the eastern part of the North Atlantic and south of 45°N, are mainly determined by the subtropical anticyclone of the Azores.
The annual average air temperatures for the coastal areas of Madeira Island are higher on the southern coast than on the northern coast and fall as you move inland according to altitude. Thus, the annual average temperature is 19.4 ºC in Lugar de Baixo (15 m), 18.8 °C in Funchal (58 m), 17.8 °C in Ponta Delgada (136 m), 15.2 ºC in Santana (380 m), dropping to 9.7 ºC in Arieiro (1,610 m). On the other islands, which are small and have lower altitudes, one can see that the average values are more uniform, in Porto Santo the average temperature is 18.7 °C.
The monthly average temperature varies little throughout the year, though it is higher during the summer (22.2 ºC in August in Funchal) and lower in winter (15.9 °C in February in Funchal).
The daily atmospheric temperature range is small, with average monthly values between 4.8 °C and 5.6 °C in Funchal, 4.6 °C and 7.9 °C in Arieiro and 4.0 °C and 5.3 °C in Porto Santo.
Sea water temperature
The monthly average temperature of sea water is relatively high and varies regularly throughout the year between about 17ºC in March and 22ºC in August and September.
The values observed for sea water temperature in the region rarely drop below 15°C and rarely exceed 25 ºC.
Relative Air Humidity
The relative air humidity is generally greater on the northern coast than on the southern coast of Madeira Island; on the other islands this variation is smaller. In the coastal regions of Madeira Island the average monthly values of relative humidity vary little throughout the year and are lower in winter than in summer.
On the island of Porto Santo, relative humidity is also higher in winter than in summer and the month of August has the lowest monthly average value.
Fogs are rare below 500m of altitude, but in the highlands (above 600m) they occur frequently, about 250 days a year.
The annual average rainfall on Madeira Island is greater on the northern coast than on the southern coast and increases with altitude; generally these values are higher on the north-facing slopes than on the south-facing ones for regions at the same altitude. Annual figures range from 553 mm in Funchal to 3,084 mm in Arieiro, 1,182 mm in Ponta Delgada and 1,527 mm in Porto Moniz.
On the other islands the amount of rainfall is lower: Porto Santo has an average annual value of 362 mm. Average monthly precipitation values vary greatly during the year, the months from October to March are the wettest, with the highest average monthly value occurring in the month of November on the south coast, and in some areas of the north coast, and sometimes in the month of January (Arieiro, Santo da Serra and Porto Moniz). On the island of Porto Santo the wettest month is January.
The annual wind regime is different on the north coast and on the south coast of Madeira Island, with prevailing winds from the NE at Ponta do Pargo (42%) and in Arieiro (40%), E in Ponta Delgada (40%) and SW in Funchal (21%), but in São Lourenço the prevailing wind is from the N (39%). In Porto Santo the prevailing wind is from the N (29%). In summer, the frequency of N and NE winds increases, passing 50% in August in Arieiro.
Insolation is the time during which the sun is shining and is expressed in decimal hours.
The monthly average insolation varies throughout the year, both in Funchal and in Porto Santo, with maximum levels in May and in August. From April to October, Funchal recorded fewer hours of sunshine than Porto Santo, a situation that is reversed in the remaining months of the year (November to March). The months with the highest values of insolation in Funchal are August (240 h) and July (228 h); December is naturally the month with the fewest hours of sunshine (140 h).
In Porto Santo, August (245 h) and May (223 h) are the months with the fewest hours of insolation. Annually, Porto Santo has more hours of sunshine (2241 h) than Funchal (2165 h), probably due to its location at lower altitudes, where cloud cover does not have as strong an influence.
On Madeira Island, cloud cover is greatest in the months from October to March and least during the months of June to August, with little variation on the north coast. In Porto Santo, the cloud cover values are higher in the winter months and lower in September. The diurnal variation of cloud cover is distinct and generally the lowest values occur during the night or morning and the highest values in the afternoon.