The Coast of Peru: from December to April summertime, temperatures from 25° to 35° C; hot and dry. There are the best months for swimming. Wintertime, May - November; the temperature drops a bit and it is cloudy. On the coast, climate is determined by cold sea-water adjoining deserts: prevailing inshore winds pick up so little moisture over the cold Peruvian current that only from May to November does it condense.
The resultant blanket of cloud and sea-mist extends from the south to about 200 km north of Lima, This garua dampens isolated coastel zones of vegetation (called lomas) and they are grazed by livestock driven down from the mountains. During the garua season, only the northern beaches near Tumbes are warm enough for pleasant swimming.
The Sierra of Peru: From April to October is the dry season. hot and day during the day, around 20° - 25° C, cold and dry at night, often below freezing. From November to April is the wet season, dry and clear most mornings, some rainfall in the afternoon, with a small temperature drop (18° C) and not much difference at night (15° C)
Peru's high season is from Jun to August, which is the best time for hiking the Inca Trail or trekking and climbing elsewhere in the country. At this time the days are generally clear and sunny, though nights can be very cold at high altitude. The highlands can be visited at other times of the year, though during the wettest months from November to April some roads become impassable and hiking trails can be very muddy.
The Jungle of Peru: April - Octuber, dry season, temperature up to 35° C. This is the best time to visit the jungle. In the jungle areas of the south, a cold front can pass through at nigh. November - Aprl, wet season, heavy rainfall at any time, humid and hot. During the wet season, it only rains for a few hours at a time, which is not enough to spoil your trip, but enough to make some roads virtually impassable.