Aveiro, where it's located

The climate of Aveiro is temperate oceanic, with mild, rainy winters and pleasantly warm, sunny summers.
The city is located on the coast of Portugal, 55 km (35 miles) south of Porto.
The average temperature of the coldest month (January) is of 10.2 °C (50 °F), that of the warmest month (August) is of 20.3 °C (68 °F). The lowest record (of the 1971/2000 period) is -3 °C (27 °F), the highest is 39 °C (102 °F). Here are the average temperatures.
Aveiro - Average temperatures
Min (°C)67910121516161512108
Max (°C)141518182023242424211815
Min (°F)434548505459616159545046
Max (°F)575964646873757575706459

Precipitation amounts to 905 millimeters (35.6 inches) per year: so, it is at an intermediate level. It ranges from 10 mm (0.4 in) in the driest month (July) to 130 mm (5.1 in) in the wettest ones (November, December). Here is the average precipitation.
Aveiro - Average precipitation

On average, there are around 2,750 sunshine hours per year: therefore, the amount of sunshine is very good. Here are the average sunshine hours per day.
Aveiro - Sunshine

The sea temperature ranges between 14 °C (57 °F) and 19 °C (66 °F). So, it never becomes warm for swimming. Here are the average sea temperatures.
Aveiro - Sea temperature
Temp (°C)141414151617181919181715
Temp (°F)575757596163646666646359


Best Time

The best time to visit Aveiro runs from June to September, since it is the warmest and the least rainy period of the year. July and August are the warmest months, but the heat is rarely excessive, and in addition, they are the driest. However, in September too, the rains are still quite rare. In May, you can go, but cool and rainy days are more frequent.
Even in summer, it's better to bring a sweatshirt, and maybe a light jacket for the evening.