The Algarve has a mediterranean climate with hot summers, and very mild winters.
From mid-May to mid-September the Algarve has almost constant sunshine with daily maximum temperatures peaking at around 27-32 degrees Celsius.
Spring and autumn are mainly sunny with the odd rainy day with maximum temperatures in the low to mid 20s Celsius. In winter there will be a rainy days, but there are plenty of warm sunny days with temperatures peaking at around 15-17 degrees Celsius.
Winter can be a fantastic time to explore the Algarve. There are periods of rain, but these generally only last a couple of days, and the majority of the time the sun shines and temperatures are pleasantly mild. It is not uncommon to see tourist visitors in shorts and t-shirts during the winter months, whereas the locals will be wearing coats and scarves!
Night times in winter can be chilly however, typically dropping to around 5-10 degrees Celsius. Although there is no frost on the coast, if you travel inland a few kilometres there can be a light frost in the early morning.
TIP: If you are travelling to the Algarve in winter, be sure to check if your accommodation has heating at night, as the houses are designed to keep the heat out.