It is quite a nice time to visit Hanoi. The rains have started, and though you may occasionally get wet, temperature-wise it is still warm and pleasant with an average temperature of 28-30°C (82-86°F). At this time, you will find wonderful green landscapes and fewer crowds than at peak tourist seasons. If you prefer to visit during dry weather, you might elect to go in late fall (October to December) or early spring (February to April).