Trujillo, where it's located

In Trujillo, Peru's third city, the climate is subtropical desert, with a warm season from January to March and a relatively cool season from June to November.
The city is located in the northern part of the Peruvian coast, in La Libertad region, and despite its location, about 8 degrees south of the Equator, the climate is arid and very mild because of the Humboldt sea current; at this latitude, the climate begins to resemble that of the Peruvian capital, Lima. The temperature range is very small: the temperature almost never drops below 10 °C (50 °F) on winter nights, while during the day, it rarely reaches 30 °C (86 °F) in the summer months. The landscape in the region is practically desert, except in areas where streams flowing from the Andes are used to irrigate fields. To find somewhat green areas, you have to go the east, at the foot of the Andes. During winter, however, moisture can condense into mists and droplets that can be deposited on the ground (a phenomenon called garúa). Some night and morning fogs can not be excluded even in summer.
Here are the average temperatures.
Trujillo - Average temperatures
Min (°C)182020181717161515151617
Max (°C)252625232322212020212223
Min (°F)646868646363615959596163
Max (°F)777977737372706868707273

The rains are definitely scarce: on average, only a few millimeters of rain fall per year, and it doesn't rain for long periods.
Here are the average precipitation.
Trujillo - Average precipitation

The climate of Trujillo is affected by the cycles of El Niño, the phenomenon consisting in an abnormal warming of the Pacific waters. In El Niño years, the temperature of the air (and also that of the sea) increases, especially in the early months of the year, when there can be long periods with almost tropical heat: for example, in February 1998, the average daily temperature has been 27.2 °C (81 °F), and in April 1983, it has been 27.5 °C (81.5 °F), with a maximum of 34.5 °C (94 °F).
In contrast, as regards to the rains, they tend to remain scarce or absent also in these periods (while more to the north, in the regions of Tumbes and Piura, and partly also in the Lambayeque Region, see Chiclayo, in El Niño years, rainfall increases as well).
During La Niña years, the phenomenon opposite to that of El Niño, the winter temperatures drop below the average, and there are long periods with highs below 20 °C (68 °F) and lows below 15 °C (59 °F).

Trujillo, Plaza de Armas

All in all, the amount of sunshine in Trujillo is decent in summer, while in winter, from June to September, it becomes quite mediocre, since the Humboldt current can cause fog and low clouds. Here are the average sunshine hours per day.
Trujillo - Sunshine

Usually, the sea in Trujillo is never very warm: it's warm enough for swimming in February and March, while it gets very cool from July to November, when it drops down to 18/19 °C (64/66 °F). Here are the average sea temperatures.
Trujillo - Sea temperature
Temp (°C)222323222020191818181921
Temp (°F)727373726868666464646670

However, in El Niño years, the sea in this area warms up a lot, especially in the early months of the year.