Flights from Launceston to San Juan lean towards being more expensive in January. Prices are generally better when you fly from Launceston to San Juan in May, with the cheapest ticket starting at $1,195.
You can imagine temperatures to be in the 32 °C range in June. The weather in San Juan is generally hotter than Launceston's. As flight availability is subject to become more limited as peak season approaches it is ideal to book in a timely manner.