We visited Calella in March a couple of years ago, weather a bit changeable, warmish during the day, chilly at night, with a couple of days of rain. Certainly not hot enough for walking around in shorts, but on sheltered balcony in sun they were fine.
If you go into Barcelona, which is a short train ride away, put your valuables inside your coat, do not put cameras on show, and hold on to your purse at all times. Mine (bright pink) was taken from my handbag, which was zipped shut, whilst we climbed onto the train -the rest of the time I had my hand over the zip but had to hold on to the handrail to climb up. The station in Barcelona is notorious for this happening, the police know it goes on, but nothing is done about it. I didn't even know it had gone till we reached the hotel.