The weather on these islands off the south coast of Vietnam is fairly difficult to predict. There are many places where weather seems to be localised and Con Dao is one of those places. If you decide to include Con Dao in your Vietnam tour package, and a good idea it is too, then you will be visiting a place that sits at the confluence of two ocean currents and that has an impact on the predictability of the weather.
The rains are usually expected in the three months of July, August and September but it would be wrong to think that they are prolonged or relentless. As a rule, they come at night-time anyway so you can expect plenty of sun if Con Dao forms part of your Vietnam holiday itinerary.
Thunderstorms are extremely infrequent despite what you might read elsewhere online. If it rains during the day, the showers will be brief and often refreshing. Vietnam is such a large country, north to south, that if you are travelling throughout the Country you will meet rain somewhere but Con Dao should not be dismissed in those three months if it suits your plans to tour then.
There is always a breeze and from November through to January that breeze becomes an easterly wind which may mean that the clarity of the sea will reduce. Occasionally, the winds cause flight delays but that is part of the experience of travelling. Con Dao is slowly being talked about outside the borders of Vietnam and you should talk to a Vietnam travel agent to learn more because you will not regret heading there any time in the year. The flight from Ho Chi Minh City is just an hour and on an organised holiday package, all the arrangements will be made for you.