Due to multiple factors, expect to potentially pay more when booking in December. For low rates, November can be a great choice for travel to Patagonia. Flights to Patagonia from Hanoi in November are about 41,158,452 ₫ on average during November, but can be found for as low as 34,799,632 ₫.
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 Aeropuerto Internacional Ezeiza/Ministro Pistarini. You can assume this to be the case over the next 18 days.
You can imagine temperatures to be in the 34 °C range in June. The weather in Aeropuerto Internacional Ezeiza/Ministro Pistarini 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.