Getting cooler

Here, in Tenerife, the weather is really nice all year round. Tourists from all over the world visit this place and enjoy the warm temperature and the sunny days. I suppose they can´t understand why the locals people are wearing sweaters when the temperature is lower than drops below 20 degrees. (what you had written was correct, but didn't sound very natural so I made a change.  Other English speakers might argue with me, but I think the correction I made feels more natural).
However, that is what happens here when autumn comes. It´s getting cooler, above all expecially at night. I mean, cooler compared to what we are used to. Some days in winter, the temperatures are below 15 degrees and we are frozen to the tourists´ astonishment.