Suriname, the former Dutch Guiana, has almost everywhere an equatorial climate, hot and humid throughout the year, with heavy rains, in fact it is covered with rainforests and mangroves.
However, in most of the country there is a rainy season from December to mid-August (with a relative decrease in February and March and a peak in May and June), and a relatively dry season from late August to mid-November.
In the capital Paramaribo, located on the coast, an average of 2,200 mm (87 in) of rain falls each year; the rainiest months are May and June, when the rainfall reaches 300 mm (12 in) per month, and when it rains almost every day. Here is the average precipitation.
Average precipitation - Paramaribo

Paramaribo	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Paramaribo	J	F	M	A	M	J	J	A	S	O	N	D	Y
Prec. (mm)	195	150	160	230	320	305	225	165	85	85	110	175	2205
Prec.(in)	7,7	5,9	6,3	9,1	12,6	12	8,9	6,5	3,3	3,3	4,3	6,9	86,8
Days	18	13	14	16	23	23	20	14	9	9	12	18	189

The rainiest regions are the east, along the Maroni River, on the border with French Guyana, where the average precipitation reaches 2,500 millimetres (98 inches) per year, and the south-central, at the foot of the Wilhelmina mountains, whose highest point is Julianatop, 1,280 metres (4,199 feet) high, where the rainfall reaches 3,000 mm (118 in) per year.
In the far south, in the Sipaliwini Savanna Nature Reserve, the dry season is longer, so the climate becomes tropical, and the region is covered by savannah, as the name suggests. Here the rainfall remains below 100 mm (4 in) per month from September to December, and just above this level in August, January and February.
As mentioned, in Suriname it's hot all year round. In Paramaribo, the average daily temperature ranges from 26 degrees Celsius (79 °F) in the coolest months (December to March), to 28 °C (82 °F) in the hottest months (September and October).
Here are the average temperatures of Paramaribo.
Average temperatures - Paramaribo

Paramaribo	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Paramaribo	J	F	M	A	M	J	J	A	S	O	N	D
Min (°C)	22	22	22	22	23	22	22	23	23	23	23	22
Max (°C)	30	30	30	31	30	31	31	32	33	33	32	30
Min (°F)	72	72	72	72	73	72	72	73	73	73	73	72
Max (°F)	86	86	86	88	86	88	88	90	91	91	90	86

The sea in Suriname is warm all year round, and its temperature is similar to the average daily air temperature on the coast, oscillating between 26 °C (79 °F) and 28 °C (82 °F).
Sea temperature - Paramaribo

Paramaribo	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Paramaribo	J	F	M	A	M	J	J	A	S	O	N	D
Sea (°C)	26	27	27	27	27	28	28	28	28	28	28	27
Sea (°F)	79	81	81	81	81	82	82	82	82	82	82	81

The amount of sunshine is not so high from December to May, while it is good in the driest period, late August to mid-November.
Sunshine - Paramaribo

Paramaribo	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Paramaribo	J	F	M	A	M	J	J	A	S	O	N	D
Sun (hours)	6	7	7	7	6	6	8	9	10	9	8	6

Suriname lies outside of the hurricane belt, because they pass over the Caribbean, hence north of the country.

When to go

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The best time to visit Suriname runs from late August to mid-November, which is the driest and sunniest; even though it is also the hottest, because here what matters most is to avoid the heavy rains.
The short dry season, in February and March, is less pronounced, but it is still quite noticeable at least along the north coast, especially from Paramaribo to the west, that is, to the border with Guyana. However, for its brevity (one or two weeks) it's not reliable.
In the far south, the Sipaliwini Savanna can be visited for a longer period, from August to February, with a preference for the period from September to December.

What to pack

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Throughout the year: tropics-friendly, loose fitting clothing, light shirts and pants of natural fibres (cotton, linen) or synthetics that breathe, maybe with long sleeves for mosquitoes; a light sweatshirt for the evening; sun hat; umbrella or light and breathable raincoat.
From December to March, a sweatshirt for the evening.