Réunion is a French Overseas Territory. There is no formal British diplomatic representation on the island. If you need consular assistance you should contact the British Embassy in Paris.
The cyclone season normally runs from December to April. See Natural Disasters
There is a low threat from terrorism. See Terrorism
Most visits to Réunion are trouble-free. Crime levels are low, but you should take sensible precautions.
Take out comprehensive travel and medical insurance before you travel.