When traveling, it's generally smart to pack in preparation for rain or any other conditions that may arise. The rainfall in Hanoi is roughly less than Salzburg. You can assume this to be the case over the next 14 days.
You can imagine temperatures to be in the 34 °C range in June. The weather in Salzburg is generally colder than Hanoi's. As flight availability is subject to become more limited as peak season approaches it is ideal to book in a timely manner.