The south is generally about 5°C (8°F) warmer than the north. The south is at its most pleasant from November to late April, before the heat of the summer becomes too oppressive.
The north is warm and sunny from October to December, before the cold and rain of winter sets in. This is the best time to visit Halong Bay, one of the natural wonders of the world. From January to March, the winter weather is unpredictable and can dampen the experience of Halong Bay considerably. The north does not get too cold in the winter, generally staying above 15°C (59°F) in the daytime.
In the centre of Vietnam there is generally more rainfall, especially in Hue from September to February. The best time to visit the centre is February to May.