Lisbon lies in both the Atlantic and Mediterranean climatic zones, thereby enjoying a pleasantly temperate climate year-round. Its mean annual temperature is 17°C (63°F), with average temperatures in winter of 13°C (55°F) and 27°C (80°F) in summer. Even when summer temperatures reach the mid-30s, the proximity of the Atlantic Ocean insures some cooling breezes. July and August are the hottest, driest months, while November to February are the wettest and coldest. The granite Serra de Sintra hosts a series of climatic phenomena that results in considerably cooler, damper conditions than in Lisbon, with frequent mists that occur even in midsummer.
| Month | Temperature | Rainfall | Humidity | Hrs of sunshine | ||
| Min | Max | AM | PM | |||
| Jan | 8 | 14 | 111 | 85 | 71 | 5 |
| Feb | 8 | 15 | 76 | 80 | 64 | 7 |
| Mar | 10 | 17 | 109 | 78 | 64 | 7 |
| Apr | 12 | 20 | 54 | 69 | 56 | 9 |
| May | 13 | 21 | 44 | 68 | 57 | 10 |
| Jun | 15 | 25 | 16 | 65 | 54 | 11 |
| Jul | 17 | 27 | 3 | 62 | 48 | 12 |
| Aug | 17 | 28 | 4 | 64 | 49 | 12 |
| Sep | 17 | 26 | 33 | 70 | 54 | 9 |
| Oct | 14 | 22 | 62 | 75 | 59 | 7 |
| Nov | 11 | 17 | 93 | 81 | 68 | 6 |
| Dec | 9 | 15 | 103 | 84 | 72 | 5 |