Map from Google - Faro

In Faro, capital of Algarve, the southernmost region of Portugal, the climate is Mediterranean, with relatively mild and rainy winters, and warm and sunny summers. There are beautiful beaches, and you can also surf in the ocean.
Here are the average temperatures.
Average temperatures - Faro
FaroJanFebMarAprMayJunJulAugSepOctNovDec
FaroJFMAMJJASOND
Min (°C)91011131418202019161310
Max (°C)151618202225282826221916
Min (°F)485052555764686866615550
Max (°F)596164687277828279726661

Precipitation is not abundant, since it's lower than 500 millimetres (20 inches) per year, and follows the Mediterranean pattern, in fact it's more abundant from October to March, while it becomes rare in April and May, and almost absent in summer.
Here is the average precipitation.
Average precipitation - Faro
FaroJanFebMarAprMayJunJulAugSepOctNovDecYear
FaroJFMAMJJASONDY
Prec. (mm)705070302051120506565447
Prec. (in)2.822.81.20.80.2000.822.62.617.6
Days76853100247750

The wind blows frequently: in the cold half-year it's related to Atlantic depressions, while in summer there are sea breezes in the afternoon.

Winter, from December to February, is mild, and is characterized by sunny periods, alternating with periods of bad weather, with wind and rain. Very cold days are rare: only in the coldest nights the temperature drops to freezing (0 °C or 32 °F), but even in these cases, during the day it typically rises above 10 °C (50 °F).

Spring, from March to May, is mild and sunny. In March and the first half of April, there may still be a bit of instability, with some rain.

Summer, from June to mid-September, is warm and sunny. Some days have an "Atlantic" weather, with highs around 25/27 °C (77/81 °F), while at other times there are hot days, with highs around 35 °C (95 °F); however, sea breezes temper the heat.

Autumn, from September to November, is initially warm and sunny. In September, the first disturbances may occur, but they are still rare. Still in October, there are many warm and sunny days, especially in the first half of the month. By November, we are well into autumn, with a mild weather, but also often cloudy and rainy.

The amount of sunshine in Faro and Algarve is excellent in late spring and summer, from May to August, while it is acceptable in autumn and winter, when in addition to sunny periods, cloudy and rainy days are possible.

Beach in Algarve

For swimming, the Atlantic Ocean is never very warm, and is still a bit cold in June, when the temperature is about 19 °C (66 °F), then it goes up to 20 °C (68 °F) in July, and to 21 °C (70 °F) in August and September.
Here are the average sea temperatures.
Sea temperature - Faro
FaroJanFebMarAprMayJunJulAugSepOctNovDec
FaroJFMAMJJASOND
Sea (°C)161516161719202121201817
Sea (°F)615961616366687070686463

When to go

The best time to visit the cities of Algarve, for walks and hikes, is the spring, in April and May.
For swimming and sun bathing the best time is instead the summer, from June to mid-September. It's better to bring a sweatshirt for cool and windy evenings, especially in June and September, but for safety also in July and August, especially if you are sensitive to cold.