Seville, where it is

The climate of Seville, capital of Andalusia, can be defined as Mediterranean, but for the torrid summer it almost seems a North African city. In fact, together with the nearby city of Córdoba, during summer Seville is the warmest city, not only in Spain but throughout Europe.
Here are the average temperatures.
Seville - Average temperatures
Min (°C)56911131720201814107
Max (°C)151720242732363632262016
Min (°F)414348525563686864575045
Max (°F)596368758190979790796861

Rainfall amounts to around 550 millimetres (21.7 inches) per year, so it's not abundant, and is concentrated, as is normal in Mediterranean climates, between autumn and early spring, while in summer it almost never rains.
Here is the average precipitation.
Seville - Average precipitation

Winter, from December to February, is mild: the average temperature is around 10/11 °C (50/52 °F). There are many sunny days, though waves of bad weather are possible, with wind and rain. Very cold days are rare, however on colder nights the temperature can drop to freezing (0 °C or 32 °F), or even a few degrees below, but during the day the temperature remains below 10 °C (50 °F) very rarely.

Spring is a bit unstable in March and at times in April, with windy days, and sometimes rainy, but it's often mild and sunny, and becomes gradually more stable and soon hot as well, before the rest of Europe. Already in April, daytime temperatures often approach 30 °C (86 °F). In May, the first torrid days can occur, especially in the second half of the month.

Summer, from June to mid-September, is hot, dry and sunny, with highs usually about 35/36 °C (95/97 °F) in July and August, but with quite frequent episodes in which they rise to around 40 °C (104 °F). In the worst times the temperature reaches 45/47 °C (113/117 °F). The sun shines regularly and the rains are very rare. In fact even September is a summer month, especially in the first half, because highs usually exceed 30 °C (86 °F) and the sun shines.
The sea is about 70 km (45 mi) away, and fortunately a bit of breeze manages to arrive here. In addition, air humidity is not high, and the daily temperature range is considerable, so that nights bring almost always a bit of relief.

Autumn, from mid-September to November, is initially hot and sunny: still in October, especially in the first part, the temperature often touches 30 °C (86 °F). But in this season the first rains begin to fall.

The amount of sunshine in Seville is great in summer, when clear skies prevail, it is good in spring, especially from mid-April onwards, and it is still fairly good in autumn and winter, when there is a moderate amount of cloudy days, during periods of bad weather, but there are also sunny periods.
Seville - Sunshine

Seville, Plaza de España

On the coast of the Atlantic Ocean, called Costa de la Luz, southwest of Seville, the sea is very cool even in summer, as the water temperature reaches a maximum of 21 °C (70 °F) in August and September. The sea creates a mild microclimate on the coast, so that when it's hot in Seville, you can find a temperature several degrees lower, and a cool breeze from the sea.
Here are the average sea temperatures (at Huelva).
Huelva - Sea temperature
Temp (°C)161516161719202121201817
Temp (°F)615961616366687070686463

When to go

The best months to visit Seville are April, May and October, to avoid both the summer heat and the winter rains, although sometimes it can rain also in these months. Those who can stand the heat can choose also the summer, being ready for the likely scorching heat.
In winter you can find many pleasant days, sunny and spring-like, although it can get cold at night, and waves of bad weather cannot be excluded.

Back to Andalusia.