In Tumbes, the climate is tropical, hot all year round, with a hotter, rainy season from January to April and a dry, relatively cool season from June to November. Usually, May and December are hot months, but with little rainfall.
Tumbes is located in the northernmost part of the Peruvian coast, near the border with Ecuador, just south of the Equator, in an area where the cold Humboldt Current arrives attenuated but is still able to influence the climate, making it drier than other areas located at the same latitude.
To the northeast of the city, on the border with Ecuador, we find the "Tumbes Mangals National Sanctuary", an area occupied by mangroves, inhabited by birds and crocodiles, while the beaches are found more to the south (see Caleta Cruz, Zorritos, Bocapán).
Here are the average temperatures.
Tumbes - Average temperatures
Min (°C)232323232221212020212122
Max (°C)323232323130292727282830
Min (°F)737373737270706868707072
Max (°F)909090908886848181828286

Normally, rainfall is not abundant, in fact, it amounts to about 460 millimeters (18 inches) per year. However, it is quite abundant in February and March, but above all, it has a strong variability. In fact, there are very dry years, when there is little rain also from January to April, and annual precipitation drops below 100 mm (4 in), normal years, when precipitation is around the average, and very wet years, when the rains become frequent and abundant, sometimes torrential, from January to May (and sometimes also in December). This happens in El Niño years, the phenomenon consisting in an abnormal warming of the Pacific waters to the west of South America, and which has significant effects in this area.
In the most intense El Niño years, the rains increase considerably, and the rainy season lasts longer, in fact, it can go from December to June or July (the temperature in these months increases as well). For example, in 1983, up to 2,210 mm (87 in) of rain fell, of which 330 mm (13 in) fell in January, when also the temperature reached 37 °C (99 °F), 350 mm (13.7 in) fell in February, 205 mm (8 in) in March, 500 mm (20 in) in April, 490 mm (19 in) in May, 115 mm (4.5 in) in June, and 165 mm (6.5 in) still in July. In 1997/1998, precipitation amounted to: 415 mm (16.5 in) already in December 1997, 470 mm (18.5 in) in January, 730 mm (28.7 in) in February (of which 240 mm or 9.4 in fell in a day), 435 mm (17 in) in March, 335 mm (13 in) in April, and 180 mm (7 in) in May, for a total of 2,565 mm (101 in) from December to May, and finally, no rain in June. In 1998, because of these heavy rains, the Tumbes River, which passes through the city and flows into the Pacific Ocean, flooded the city.
Here, however, is the average rainfall.
Tumbes - Average precipitation

Zorritos Beach

The amount of sunshine in Tumbes is not very good, however, the sky tends paradoxically to be cloudy especially in the cooler and dry period, from July to September, while in the rainy season, there is an alternation between sunshine and cloudiness. The sunniest month is December, with about 7 hours of sunshine per day. Here are the average sunshine hours per day.
Tumbes - Sunshine

The sea in Tumbes is warm enough for swimming from January to May, while it becomes a little cool from July to November. However, given the latitude, it is cooler than in other parts of the world. Here are the average sea temperatures.
Tumbes - Sea temperature
Temp (°C)242525242423222121212223
Temp (°F)757777757573727070707273

In El Niño years, the sea in this area warms up a lot, so much so that it can reach 29 °C (84 °F) in the early months of the year.