The climate of the Cinque Terre is tempered, favoured by the mountains that shelter from the northern winds. The Mediterranean Sea mitigates the winter season with an average temperature of 12-14 degrees. In summer, the average temperature reaches 30 degrees.
Best time to visit this part of Italy is from mid March to late October, but even in winter you will find tourists. The best months for hiking are April, May, June, September or October. In July and August the weather is hot with little rainfall.
If you are hiking in this period try to head out in the morning to avoid the midday sun and the many tourists who arrive in the afternoon.
When you visit the Cinque Terre during the summer months keep in mind that July and August is the peak tourist season and it is advisable to book accommodation in advance.
For more details on weather conditions and average annual temperatures you can visit the page Weather.