July is in the "winter" season in Mauritius. Since the hotel is on the North West part of the island you will benefit from the sun set. You may be unlucky to have some rain but since it is not during the cyclonic period ( end of december to march) there is nothing to fear. The water temp should be around 19 to 22 celsius. Have not stayed at the Oberoi ( relatives have a bungalow near pte aux cannoniers in the north) but it is along a bay.

Enjoy your stay and don't forget to visit the Market in Port-Louis ( bus ride or taxi)