Climate and Average Weather Year Round in French Guiana French Guiana

The climate in French Guiana is hot, oppressive, and mostly cloudy. Over the course of the year, the temperature typically varies from 72°F to 89°F and is rarely below 71°F or above 91°F.

Based on the beach/pool score, the best time of year to visit French Guiana for hot-weather activities is from mid July to mid October.

The temperature in French Guiana varies so little throughout the year that it is not entirely meaningful to discuss hot and cold seasons.

In French Guiana, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.

The clearer part of the year in French Guiana begins around June 18 and lasts for 3.8 months, ending around October 10.

The clearest month of the year in French Guiana is August, during which on average the sky is clear, mostly clear, or partly cloudy 56% of the time.

The cloudier part of the year begins around October 10 and lasts for 8.2 months, ending around June 18.

The cloudiest month of the year in French Guiana is May, during which on average the sky is overcast or mostly cloudy 75% of the time.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in French Guiana varies very significantly throughout the year.

The wetter season lasts 8.1 months, from November 30 to August 2, with a greater than 58% chance of a given day being a wet day. The month with the most wet days in French Guiana is June, with an average of 27.1 days with at least 0.04 inches of precipitation.

The drier season lasts 3.9 months, from August 2 to November 30. The month with the fewest wet days in French Guiana is September, with an average of 7.5 days with at least 0.04 inches of precipitation.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. The month with the most days of rain alone in French Guiana is June, with an average of 27.1 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 93% on May 28.

Rainfall

To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. French Guiana experiences extreme seasonal variation in monthly rainfall.

Rain falls throughout the year in French Guiana. The month with the most rain in French Guiana is May, with an average rainfall of 17.4 inches.

The month with the least rain in French Guiana is September, with an average rainfall of 1.4 inches.

The length of the day in French Guiana does not vary substantially over the course of the year, staying within 21 minutes of 12 hours throughout. In 2024, the shortest day is December 21, with 11 hours, 54 minutes of daylight; the longest day is June 20, with 12 hours, 21 minutes of daylight.

The earliest sunrise is at 6:16 AM on October 26, and the latest sunrise is 31 minutes later at 6:47 AM on February 4. The earliest sunset is at 6:14 PM on November 7, and the latest sunset is 34 minutes later at 6:48 PM on July 18.

Daylight saving time (DST) is not observed in French Guiana during 2024.

The figure below presents a compact representation of key lunar data for 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases.

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

The perceived humidity level in French Guiana, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, remaining a virtually constant 100% throughout.

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in French Guiana experiences mild seasonal variation over the course of the year.

The windier part of the year lasts for 5.4 months, from December 4 to May 16, with average wind speeds of more than 6.1 miles per hour. The windiest month of the year in French Guiana is February, with an average hourly wind speed of 7.3 miles per hour.

The calmer time of year lasts for 6.6 months, from May 16 to December 4. The calmest month of the year in French Guiana is July, with an average hourly wind speed of 4.9 miles per hour.

The predominant average hourly wind direction in French Guiana is from the east throughout the year.

French Guiana is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.

The average water temperature does not vary significantly over the course of the year, remaining within 1°F of 81°F throughout.

To characterize how pleasant the weather is in French Guiana throughout the year, we compute two travel scores.

The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit French Guiana for general outdoor tourist activities is from early July to late September, with a peak score in the second week of August.

The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit French Guiana for hot-weather activities is from mid July to mid October, with a peak score in the third week of August.

Methodology

For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.

Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.

Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.

Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.

Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

Temperatures in French Guiana are sufficiently warm year round that it is not entirely meaningful to discuss the growing season in these terms. We nevertheless include the chart below as an illustration of the distribution of temperatures experienced throughout the year.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy experiences some seasonal variation over the course of the year.

The brighter period of the year lasts for 2.3 months, from August 10 to October 20, with an average daily incident shortwave energy per square meter above 6.1 kWh. The brightest month of the year in French Guiana is September, with an average of 6.4 kWh.

The darker period of the year lasts for 1.3 months, from May 11 to June 22, with an average daily incident shortwave energy per square meter below 5.0 kWh. The darkest month of the year in French Guiana is June, with an average of 4.9 kWh.

For the purposes of this report, the geographical coordinates of French Guiana are 4.000 deg latitude, -53.000 deg longitude, and 0 ft elevation.

The topography within 2 miles of French Guiana is essentially flat, with a maximum elevation change of 0 feet and an average elevation above sea level of 0 feet. Within 10 miles is also essentially flat (0 feet). Within 50 miles is also essentially flat (0 feet).

The area within 2 miles of French Guiana is covered by trees (100%), within 10 miles by trees (99%), and within 50 miles by trees (97%).