The Amazon Rainforest is defined by a consistent climate of heat, moisture, and high humidity. Spanning nine nations in South America, its weather system influences global climate patterns. The average weather here is a tropical wet climate, where seasonal changes are marked by variations in rainfall rather than temperature shifts familiar to temperate regions.
Consistent Tropical Temperatures
The average air temperature in the Amazon basin is stable across the calendar year, hovering between 75°F and 85°F (24°C and 29°C) across the vast majority of the region. This uniformity is a defining characteristic of an equatorial climate, where the angle of the sun changes very little throughout the year. Unlike locations at higher latitudes, the Amazon does not experience four distinct seasons with significant temperature swings. The lack of seasonal thermal variation ensures a near-constant growing environment for the forest’s immense biodiversity.
Daily temperature cycles, known as the diurnal range, are often more pronounced than the monthly or seasonal shifts. While the average daytime high can reach up to the mid-90s F (mid-30s C), the temperature frequently drops by 15 to 20 degrees Fahrenheit after sunset and during heavy rainfall. This daily cooling moderates both the highest daytime temperatures and the nighttime lows. The forest floor, protected by the canopy, generally experiences a cooler, more buffered temperature environment compared to the air above the trees.
Defining the Wet and Dry Seasons
Precipitation is the primary factor that dictates the rhythm of the Amazon’s climate, which is divided into a wet season and a “dry” season. The term “dry season” simply refers to a period of relatively reduced rainfall, not a period without rain, when compared to arid climates. The Amazon receives high annual rainfall, typically ranging from 80 to 120 inches (2,000 to 3,000 millimeters) across the basin. This moisture supports the dense, lush vegetation.
The wet season generally runs from December or January through May or June, characterized by daily, intense, and prolonged downpours. During this time, the Amazon River and its tributaries swell dramatically, flooding vast areas of the surrounding forest. This high-water period is crucial for the reproductive cycles of numerous aquatic and terrestrial species. The air maintains consistently high relative humidity levels, often averaging between 77% during the drier months and over 88% during the peak of the wet season.
The dry season runs roughly from July or August through November or December, seeing a reduction in the frequency and intensity of rain showers. Even during this period, rain still falls regularly, but the total monthly accumulation is significantly less than in the wet season. This decrease in precipitation causes river levels to drop, exposing sandbanks and creating new terrestrial habitats. The high humidity persists year-round, ensuring the forest remains a moist, tropical environment.
Regional Weather Variation and Climate Drivers
The immense scale of the Amazon basin means that weather conditions are not entirely uniform, exhibiting regional variations influenced by geography and atmospheric circulation. The western Amazon, particularly areas closer to the Andes Mountains, experiences higher annual rainfall totals due to the orographic effect. These regions, such as parts of the Peruvian Amazon, also tend to be slightly cooler and have less pronounced seasonal differences in precipitation.
In contrast, the central and eastern portions of the basin, located farther from the Andean moisture source, display a more distinct contrast between the wet and dry periods. Areas near the Atlantic coast may experience a stronger dry season with a more significant reduction in monthly rainfall. These differences in rain distribution are governed by the movement of the Intertropical Convergence Zone (ITCZ), a band of low pressure that circles the Earth near the equator. The seasonal migration of the ITCZ dictates the timing of the wet season across different parts of the basin.
Moisture is also maintained by evapotranspiration, where the forest itself recycles vast amounts of water back into the atmosphere. Plants release water vapor through their leaves, which then condenses to form clouds and precipitation. This biological mechanism accounts for a substantial portion of the Amazon’s total rainfall, sustaining the regional climate.