In terms of weather, Cartagena is always sunny and warm (hot). “Rainy Season” is defined by a few light sun showers around September and October. If you’re looking for a city that parties all night, then December is your month. The end of December through New Year’s is a time you must witness for yourself. From the lights in the Old City to the non-stop parties and events, everyone finds something to do in Cartagena during this time.