We will be on your cruise.
It will be hot at the beginning and at the end. It can be quite cold AND windy down south... So, have a good water-resistant windbreaker, lighter jacket and sweater, with warm pants, hat and gloves for those excursions on or near the water--Layering is the key; if it warms up, take off layers as needed. In Santiago and Buenos Aires it will be very hot. Shorts, tee-shirt and sandals, or light dresses during the day... comfortable shoes! Light-weight dressier clothes at night, but no fancy jewelry or cameras. Stay alert and have fun!