Map from Google - Alicante

In Alicante, a city on the southeastern coast of Spain, the climate is Mediterranean, with mild and relatively rainy winters, and hot and sunny summers. The city is located in a particularly mild area, dry and sunny.
The average temperature of January is 11.5 °C, that of August is 26 °C. Here are the average temperatures.
Average temperatures - Alicante
AlicanteJanFebMarAprMayJunJulAugSepOctNovDec
AlicanteJFMAMJJASOND
Min (°C)77911141821221915118
Max (°C)171719212428303129252017

The rains are scarce, just 285 millimetres per year; in particular, winter is drier than it normally is in Mediterranean climates; in summer it almost never rains. Rainy days are particularly rare, but when it rains it can rain a lot, and sometimes the rains may be intense and concentrated in time, causing floods. Due to the scarcity of rainfall, the landscape is arid.
Here is the average precipitation.
Average precipitation - Alicante
AlicanteJanFebMarAprMayJunJulAugSepOctNovDecYear
AlicanteJFMAMJJASONDY
Prec. (mm)2020203030104540453525285
Days43344211444437

Winter, from December to February, is mild, and is characterized by sunny periods, alternating with rare periods of bad weather, with wind and rain. There are many sunny days in which the daytime temperature reaches or exceeds 20 degrees, even in winter. Very cold days are rare: only on colder nights the temperature drops to freezing, but even in these cases, usually the daytime temperature rises above 10 degrees. In practice, it never snows.

Spring, from March to May, is mild and sunny, with rainy days still possible, but not very frequent, and some afternoon thunderstorms coming from the interior in late spring. Starting in May, and sometimes in April, you begin to see the first warm days, with highs around 30 °C.

Summer, from June to mid-September, is hot and sunny. Typically, maximum temperatures hover about 28/29 degrees in June and September, and 30/32 °C in July and August, there's a quite humid heat but also the sea breeze, in short, the typical Mediterranean summer. However, sometimes there may be heat waves, during which temperatures can touch 35/37 degrees, and sometimes even 40 °C.

Autumn, from mid-September to November, is initially warm, then gradually becomes milder, and Atlantic weather fronts become gradually more frequent. Occasionally, the rains are concentrated in a short time and can be heavy.

The amount of sunshine in Alicante is very good in the summer, when clear skies prevail, but it is good also in the other seasons: there's an average of 6 hours of sunshine a day even from November to January, and 7 in February.

Alicante

The sea in Alicante is warm enough for swimming from July to September, when it reaches 25/26 degrees (ie, more than in other parts of Spain); in June and October it is cool. Here is the temperature of the sea.
Sea temperature - Alicante
AlicanteJanFebMarAprMayJunJulAugSepOctNovDec
AlicanteJFMAMJJASOND
Sea (°C)151414161922252625231917

When to go

The best time for a beach holiday in Alicante is the summer, from June to August. For swimming, the best time is from July to September, although from September, which overall is still a good month (especially in the first half), the first Atlantic frontal systems may pass. May and June are the sunniest months, but the sea is still a bit cool, especially in May, when it is actually a bit cold.
Although good weather is not always guaranteed, spring and autumn are ideal for visiting the city and making excursions in the interior, as in summer it can be very hot.