It could be a hot beautiful sunny morning, without a cloud in the sky, but by the time I get to school it could be raining and freezing cold. It does not rain for long but it might rain a few times during the day and when it does it gets very chilly.
During rainy season it is wise to carry a sweater and a rain coat with you at all times because you just never know when it will rain.
...I may or may not have learned this the hard way :)