The central and southern coast has a subtropical desert climate, although this region is located in the tropics. The Humboldt Current is 7 °C (12.6 °F) to 8 °C (14.4 °F) colder than normal tropical seas at 14 to 19 °C (57.2 to 66.2 °F), so this prevents high tropical temperatures from appearing.
Moreover, the Andes mountains are very close to the coast, so this prevents cumulus clouds or cumulonimbus clouds from appearing. Therefore, a shade effect is created, and there are only few annual rainfalls in this region.
Rainfall averages 5 mm (0.2 in)/yr near the Chilean border to 200 mm (7.9 in)/yr in the northern coast and near the Andes.
The central coast is composed of regions like La Libertad, Ancash and Lima, having a spring-like climate for most of the year. Foggy and sunny days intermingle around the humid sand dunes most of the year.
Most summers (January–April) have pleasant temperatures from 19 to 21 °C (66.2 to 69.8 °F) during the nights to about 28 to 29 °C (82.4 to 84.2 °F) during daytime. Winters (June–October) are very humid, and range from 12 to 15 °C (53.6 to 59 °F) during the nights to around the 17 to 18 °C (62.6 to 64.4 °F) during the day.
The spring and autumn months have a pleasant climate that ranges from 23 °C (73.4 °F) during the day to around 17 °C (62.6 °F) during the night. As you go inland, away from the coast and on to the yunga valleys the climate is drier and warmer during all seasons: around 3 °C (5.4 °F) warmer in any given month.
Strangely enough, it also gets warmer if you go north of Lima into La Libertad or Ancash or south of Lima (Pisco, Chincha), at least during the day. The reason is probably since Lima is located where the Humboldt current prevails, yet there are tropical sun rays above the clouds that create fog and since there is no passage of hot clouds from the Amazon to the coast, the climate is cooler that similar tropical latitudes. This created a lot of humidity and fog in winter times.
The southern coast composed of Ica, Arequipa, Moquegua and Tacna regions have a drier and warmer climate during the day-time for all months except for winters. There are regions famous for their sand dunes and impressive deserts since the climate is drier and hotter. The temperatures can go as high as 36 °C (96.8 °F) in the Nazca and regions inland, yet can fall to 8 or 9 °C (46.4 or 48.2 °F) during the winter months. During the daytime temperatures rarely go below the 22 or 23 °C (71.6 or 73.4 °F) for all months. These fact determine that the southern coast have a semi Mediterranean desert like climate yet there is small variations between temperatures during night time or day time, as regions in tropical latitudes. Clear skies are for the most part attractive near the coastal cliffs, home to a variety of fish and marine mammals.