When travelling, it's generally smart to pack in preparation for rain or any other conditions that may arise. The rainfall in St John is roughly similar to Cleveland. You can assume this to be the case over the next 19 days.
You can imagine temperatures to be in the 29 °C range in July. The weather in Cleveland is generally hotter than St John's. As flight availability is subject to become more limited as peak season approaches it is ideal to book in a timely manner.