The climate is tropical and humid. The seasons are the opposite to the UK but the sea temperature rarely drops below 23°C! The summer from December to March with an average temperature of 26°C on the coast. Winter is from April to November with an average temperature of 20°C on the coast. However, as one moves inland, and up, the temperature drops progressively - so, do not forget some warm clothing if you intend to trek the cirques. It actually snowed in the 'heights' in October 2006 and for once the "Piton des Neiges" at 3072 metres lived up to its name.
The cyclone season is usually between December and February and on the rare occassion that a cyclone comes close enough to be a threat one is always alerted well in advance.
Take a look at the weather here for an overview and up to date information concerning tropical storms.
Being an island situated in the Indian Ocean, Réunion has very much a maritime climate. The prevailing winds blow from the east and south-east - the west coast being known as the leeward coast. On days when one needs a break from the beach, a trip up into the 'Hauts" with a refreshing breeze is ideal.
The east coast has, generally, more rain than the west but for a small island nothing is ever quite that simple. The are many 'micro-climates' throughout the island and one can be sure to find one that is suitable.