Tralee has a maritime temperate climate: mild winters, cool summers, and rain distributed fairly evenly throughout the year with a slight bias toward autumn. Average July temperatures are around 17°C; January averages around 6°C. The Gulf Stream keeps the winters much milder than the latitude would suggest.
The best time for outdoor activity — hiking the Dingle or Ring of Kerry — is May to September, when the days are longest and the weather most settled (though "settled" is relative in Kerry). July and August are the busiest months for tourism and correspondingly harder for finding accommodation.
Rose of Tralee Festival: The last week of August, usually centred on the Bank Holiday weekend. This nationally televised competition and festival fills every pub, B&B, and street in the town with enormous crowds. Either plan around it or embrace it: it is genuinely entertaining if you enjoy the particular flavour of Irish festivities, but trying to visit Tralee quietly that week is not possible.