The climate of French Guiana is wet from January to June. It receives very heavy rainfall during May. The dry season is from July to December. This is considered to be the best time to visit as the climate of French Guiana is comfortable during the dry season.
However, right round the year, the weather is hot and humid. The average temperature during the year is around 82 degrees Fahrenheit or 28 degrees Celsius. So, it is best to carry light clothing. It is also advisable to carry some rainwear just in case you need it.