We went in February and it was quite hot....so shorts and t shirts on the ship but loose, cotton/linen skirts/trousers when ashore keeping shoulders covered and if visiting holy sites covered from head to toe ....Costa is quite an informal cruise line so only need suit, or Blazer shirt and tie for dining, tops and trousers/skirts for ladies are quite acceptable. Hope this helps a bit but a bit more info on when you are going would have helped!!
Now ....are you male or female, do you have an extensive wardrobe, where apart from Dubai are you going, when are you going, are you expecting to spend most of your time sunbathing or sight-seeing, how old are you, do you like sailing, are you likely to go snorkelling, do you intend to fully subscribe to the ship's dress code, will you be visiting religious establishments, or camel riding and do you think that you will be taking a spaghetti spoon with you? Please answer soon as I am intrigued by you and this question .....Neil.