French Guiana Weather: A Year-Round Guide to the Tropics

The Equatorial Rhythm: Understanding the Climate

French Guiana is defined by a classic equatorial climate (Köppen Af), characterized by high heat, consistent humidity, and heavy rainfall. Located between 2° and 6° north of the equator, the region does not experience traditional thermal seasons like autumn or winter. Instead, the year is dictated by the movement of the Intertropical Convergence Zone (ITCZ), a massive belt of low pressure that brings alternating periods of torrential rain and intense sun.

The Four Seasons of French Guiana

Locals generally divide the year into four distinct phases based on moisture levels rather than temperature changes:

• The Big Rainy Season (Mid-April to June): This is the wettest part of the year. Rainfall is heavy and frequent, peaking in May with monthly averages often exceeding 500mm (20 inches). Humidity is at its most oppressive, often staying above 90%.
• The Big Dry Season (July to November): Known as the most pleasant time for travel, this period sees the highest temperatures (peaking in September and October at 32°C/90°F) but significantly less rain. Humidity levels drop slightly, and the sun shines for an average of 7-8 hours per day.
• The Small Rainy Season (December to February): Shorter, intense downpours return as the ITCZ moves south. While wet, it is interspersed with sunny intervals, though the sea can become rougher during this time due to the strengthening of the northeast trade winds (the Alizés).
• The Small Summer of March (March to Mid-April): A brief, unreliable dry spell that provides a temporary reprieve from the rains. It is more noticeable in the northwest, near Saint-Laurent-du-Maroni, than in the east.

Daily Weather Evolution

A typical day in French Guiana follows a predictable cycle. Mornings often begin clear and bright, though very humid. As the sun heats the surrounding rainforest, moisture rises, leading to the formation of towering cumulus clouds. By mid-afternoon, these frequently result in short, violent thunderstorms. Evenings often cool slightly as a breeze develops, though "cool" in this context rarely means dropping below 23°C (73°F).

Regional Variations and Microclimates

Despite its small size, geography creates subtle weather divides:

• The Coastal Belt: Cities like Cayenne and Kourou benefit from the Alizés (trade winds), which provide a cooling effect that makes the heat more manageable than in the interior.
• The Amazonian Interior: Away from the coast, the wind drops, and the air becomes stagnant and sweltering. Temperatures can reach 37°C (99°F) in the depths of the jungle.
• The East-West Gradient: The eastern part of the territory (near Brazil) tends to be wetter than the west (near Suriname), where the dry seasons are often more pronounced and reliable.

Historical Context and Local Adaptation

Historically, French Guiana has been free from the tropical cyclones and hurricanes that plague the nearby Caribbean, as it sits too close to the equator for the necessary Coriolis effect to form such storms. However, recent data suggests a slight warming trend, with historical mean temperatures rising by nearly 1°C over the last 50 years.

Locals have adapted to this "eternal summer" through architecture and lifestyle. High ceilings and shutters for cross-ventilation are standard in older Creole houses to combat humidity. The "feel" of the weather is often described as lourde (heavy), a physical weight of moisture that forces a slower, more deliberate pace of life, particularly during the humid peaks of the afternoon.

Phenomenon: The ITCZ and "Grain"

One specific phenomenon to watch for is the grain—a sudden, localized squall characterized by a sharp increase in wind and a wall of rain. These can move rapidly across the landscape, turning a sunny afternoon into a deluge in minutes before disappearing just as quickly.