In Guyana (formerly British Guiana), a South American country which overlooks the Atlantic Ocean in the north and touches the Equator in the extreme south, the climate is hot and humid all year round.
As regards to the rainfall, there are two rainy seasons (from December to early February and from late April to mid-August) and two relatively dry seasons (typically, February-March and September-October). Both duration and intensity of rainfall vary depending on area, but the period May-August is very rainy everywhere. In the areas that don't have a real dry season, we can speak of equatorial climate, otherwise, of tropical climate. The rains mainly occur in the form of heavy showers and thunderstorms, usually in the afternoon or evening.

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The forest



Most of Guyana is occupied by the forest, which means that the rains are constant throughout the year, or that there are short and not very pronounced dry seasons.

Georgetown

In the capital, Georgetown, as in the rest of the country, the temperature is fairly constant throughout the year; daytime temperatures are slightly higher in September and October and slightly lower in the period from December to March. At least, in the capital, as generally happens along the coast, the heat of the day is cooled by the ocean breeze. Here are the average temperatures.
Georgetown - Average temperatures
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)242424252524242425252424
Max (°C)292929303029303031313029
Min (°F)757575777775757577777575
Max (°F)848484868684868688888684

In the central-eastern parts of the coast, where Georgetown is located, between the two relatively dry seasons, in September-October (when 90/95 mm or 3.5/3.7 inches of rain fall per month), it rains just a little less than in February-March, so the difference is not significant. Here, therefore, there is no real dry season. In Georgetown, 2,400 mm (94.5 in) of rain fall per year. The wettest month is June, with 345 mm (13.5 in) of rain. Here is the average precipitation.
Georgetown - Average precipitation
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec.(mm)25012011518029534528018590951503152420
Prec.(in)9.84.74.57.111.613.6117.33.53.75.912.495.3
Days1713121220232116791020180

Guyana does not get a lot of sun in the rainy months, while in the dry periods, the sky is usually clear, even though a bit of cloudiness may develop at any time. Here are the average sunshine hours in Georgetown.
Georgetown - Sunshine
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Hours677765788876

The sea in Guyana is warm enough for swimming all year round, in fact, the water temperature ranges from 26 °C (79 °F) to 28 °C (82 °F), as can be seen from the sea temperature near Georgetown.
Georgetown - Sea temperature
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Temp (°C)272627272727282828282827
Temp (°F)817981818181828282828281

In the other coastal areas of Guyana, it is hot all year round as in the capital, but the rains follow a slightly different pattern depending on the area.

Mabaruma

In the north-west, there is no real dry season, but only a relative decrease in precipitation: here, even September and October are quite rainy, with around 200 millimeters (8 inches) of rain per month, while from February to mid-April, when around 100 mm (4 in) of rain fall per month, the decrease in rainfall is more noticeable. Here is the average precipitation.
Mabaruma - Average precipitation
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec.(mm)195851051602804103602552102152953002875
Prec.(in)7.73.34.16.31116.114.2108.38.511.611.8113.2
Days181011101923252413181720208

New Amsterdam

In the easternmost part of Guyana, near the border with Suriname, the second relatively dry season is longer and a bit more pronounced, and also includes the month of November.
Here is the average precipitation in New Amsterdam.
New Amsterdam - Average precipitation
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec.(mm)22514013518028529516516560701002502175
Prec.(in)8.95.55.37.111.211.66.56.52.42.83.99.885.6
Days20121214191818159101219178

The savanna



In the south-west, towards the border with the Brazilian state of Roraima, we find the area of the savannah, where the climate is tropical, with a dry season from October to March, characterized by intense heat, with highs around 33/35 °C (91/95 °F).

Lethem

Here are the average temperatures of Lethem.
Lethem - Average temperatures
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)232324242423232323252424
Max (°C)323333323130303133343333
Min (°F)737375757573737373777575
Max (°F)909191908886868891939191

Although the total quantity of rainfall in this area is high, around 1,700 mm (67 in), there is a single and long dry season which goes October to March, with poor rains, around 30 mm (1.2 in) per month, from November to March, and 50 mm (2 in) in October. In April and September, the rains are moderate, while they are heavy from May to August.
Here is the average precipitation.
Lethem - Average precipitation
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec.(mm)303030110300375340275805035251680
Prec.(in)1.21.21.24.311.814.813.410.83.121.4166.1
Days656102123222111965145

In addition to the strip along the border where Lethem is located, called North Rupununi Savannah, there is a more extensive area of savannah, called South Rupununi Savannah, located south of the Kanuku Mountains (a low mountain range covered by forests).

North of the Rupununi Savannahs, there is a mountain range, the Sierra Pacaraima, culminating in Mount Roraima, which has its summit in Venezuela, but which exceeds 2,200 meters (7,200 ft) in the Guyanese part. Other peaks are Mount Ayanganna, 2,041 meters (6,696 feet) high, and Mount Caburaì, 1,465 meters (4,806 feet) high. Obviously, the temperature decreases with increasing altitude, and although we are near the Equator, the air is cool above 1,500 meters (5,000 feet). On the northern slopes of this mountain range, precipitation reaches 3,500 mm (138 in) per year. In these mountains, the Potaro River, which then feeds the huge and spectacular Kaieteur Falls, has its source.

Kaieteur Falls

Hurricanes



Guyana is outside of the path of hurricanes, which pass to the north, on the Caribbean Sea, however, it can not be ruled out that some of the rare hurricanes that pass at a very low latitude, affecting Trinidad and Tobago and the northeastern coast of Venezuela, may also produce some effects on Guyana, in terms of rain and anomalous waves on the coast, especially in the northernmost part. The hurricane season in the Caribbean goes from June to November, though they are more likely from August to October.

Best Time



The best time to visit Guyana depends mainly on the rain pattern, which, as we said before, is not the same throughout the country. In the north-west (see Mabaruma), the best period is February-March. In Georgetown and in the central area, the best periods are September-October and February-March. In the east, the best period is September-October, but it extends until November (so, it goes from September to November). In the south-western area of the savannah (see Lethem), you can go from October to March.
If you want to choose a single period for the whole country, you can choose February and March.

What to pack



Throughout the year: bring lightweight clothing of natural fibers, possibly with long sleeves for mosquitoes; a light sweatshirt, a sun hat, and an umbrella or a lightweight, breathable raincoat.
When going mountain climbing, bring hiking shoes and a sweatshirt.
From December to March, add a sweatshirt for the evening.