About the Weather
Lima and all peruvian coast offers the four common seasons Lima. It is summer from January to March. During the summer the temperature varies from 20°C to 28°C. You must consider that relative humidity in Lima is high (80% to 98%) and warm feeling is also high.
Seasons and temperatures of other cities outside the peruvian coast are completely different. For instance, highland cities are in the "andean winter" season and temperature is very low (Cusco is a highland city).
For further information about the weather, you can visit the Web page of Servicio Nacional de Meteorología e Hidrología del Perú