At this time, Cheapflights has noticed price decreases for many domestic flights due to COVID-19. Travel is not necessarily recommended at this time, and flights may be prone to cancellation: please check with local authorities in both Dublin and Portsmouth for travel alerts, and be sure to review the airline's cancellation policy and travel advisories before booking. For more information, please view our post on what to know about COVID-19 (coronavirus) and travel.
When travelling, it's generally smart to pack in preparation for rain or any other conditions that may arise. The rainfall in Dublin is roughly less than Portsmouth. You can assume this to be the case over the next 24 days.
You can imagine temperatures to be in the 29 °C range in July. The weather in Portsmouth is generally hotter than Dublin's. As flight availability is subject to become more limited as peak season approaches it is ideal to book in a timely manner.