Map from Google - Seychelles

In the Seychelles the climate is tropical, hot all year round, with a rainy and muggy season from December to March, due to the northwest monsoon, and a dry and slightly cooler season from June to September, when southeast trade winds prevail. Even in the dry season, however, sometimes it can rain.
There is little diurnal and annual variation in temperature, so that the temperature rarely exceeds 32 °C (90 °F) during the day, or drops below 20 °C (68 °F) at night.
The tropical rains occur mainly in the form of downpour or thunderstorm, and in the Seychelles they often occur in the evening or at night; in the rainy season, however, cloudiness is more frequent even during the day.
Seychelles is an archipelago of more than a hundred islands, islets and atolls, scattered over a wide area, even 1,200 kilometres (750 miles) long, in the Indian Ocean, therefore, although they have a fairly homogeneous climate, there are still some differences. The islands can be divided into two groups: in the north we find the Inner Islands (area 1 on the map), which include the so-called Granitic Seychelles, the largest and most densely populated (Mahé, where the capital Victoria is located, Praslin and La Digue); in the south we find the Outer Islands (area 2 on the map), which extend towards the south-west and are flat coral atolls.

Geographical division of the Seychelles

The Seychelles are close to the Equator, in fact their latitude ranges from 3 to 10 degrees south, which means that the day lasts about 12 hours all year round, and the sunset comes quite early, between 6 and 6:30 p.m.
The average daily temperature ranges from 26 °C (79 °F) in July and August, to 27 °C (81 °F) in January, to 28 °C (82 °F) in March, April and May, which are the warmest months. The coolest months, July and August, are the acme of the south-east trade winds period, which goes from May to October. In this period, the wind can make the sea rough, especially along the coasts exposed to the east and south; the wind reaches its peak in August, with gusts of 50/60 kph (30/37 mph), and can bring seaweed to the shore and create dangerous currents near the most exposed coasts.
Here are the average temperatures of the capital Victoria.
Average temperatures - Victoria
VictoriaJanFebMarAprMayJunJulAugSepOctNovDec
VictoriaJFMAMJJASOND
Min (°C)242525252525242424242424
Max (°C)303031313129282829303030
Min (°F)757777777777757575757575
Max (°F)868688888884828284868686

As regards the rains, the northern islands (therefore closer to the Equator) are generally rainier than the southern ones. Mahé, the main island, at a latitude of 4° S, is the rainiest. In Victoria, 2,200 millimetres (85 inches) of rain per year fall, with more than 250 mm (10 in) per month from December to February, and less than 100 mm (4 in) per month from June to August. In the interior of the main island, there are some hills, along whose slopes the annual rainfall reaches 3,500 mm (138 in). The driest areas of the island are the north and south sides, where the rainfall drops below 2,000 mm (79 in) per year.
Here is the average precipitation in Victoria.
Average precipitation - Victoria
VictoriaJanFebMarAprMayJunJulAugSepOctNovDecYear
VictoriaJFMAMJJASONDY
Prec. (mm)3802601651751256580951202052152802165
Prec.(in)1510,26,56,94,92,63,13,74,78,18,51185,2
Days171111141110101011121418149

The northernmost islands, at a latitude of 3° S, are Bird Island, with an annual average precipitation of 1,950 mm (77 in), and Denis Island, which receives 1,700 mm (67 in). The southernmost of the Outer Islands are drier, in particular the Farquhar Group, and even more so the Aldabra Group in the south-west, so that in the island of the same name, rainfall drops to 985 mm (38.5 in) per year, and in the smaller island of Assumption, to only 865 mm (34 in).
The rain pattern in the Seychelles is quite erratic from year to year, in particular they may be affected by the so-called ENSO cycle: in the years of El Niño, sometimes it rains a lot during the dry season, and the rainy season is drier than normal, while in the years of La Niña, the opposite happens.
The northernmost islands, including Mahé, are too close to the Equator to be directly affected by tropical cyclones, however, they can be brushed by cyclones that form south of the Equator in the period November to mid-May, and more frequently from January to mid-April. Cyclones bring strong winds and torrential rains. On the contrary, the southernmost of the Outer Islands, especially the groups of Aldabra and Farquhar, are located in the path of cyclones.

Seychelles

In the Seychelles, the temperature of the Indian Ocean is always warm enough for swimming, ranging between 26 °C (79 °F) in July and August, and 30 °C (86 °F) in April.
Sea temperature - Victoria
VictoriaJanFebMarAprMayJunJulAugSepOctNovDec
VictoriaJFMAMJJASOND
Sea (°C)282929302927262627282828
Sea (°F)828484868481797981828282

When to go

In the Seychelles, the less sultry period, and also the driest and sunniest, is the southeast trade winds season, from May to September, and in particular from June to August, but at this time the wind can be moderate and make the seas rough. The wind reaches its maximum intensity in July and August. In this period, the beaches exposed to the north-west (eg the beach of Beau Vallon in Mahe) will therefore be preferable. The period from March to May is the hottest of the year, albeit slightly, and there is the risk of some heavy rainstorms but especially the passage of cyclones, which however affect only marginally the main islands of the north; the month of October, before the rainy season, is also exposed to heavy showers, but at least it is outside the cyclone season. The relatively worst months are December and January, being the most sultry and rainy, as well as the least sunny, even though the sun shines for a few hours a day.

What to pack

In winter (June to August): light clothes, light sweatshirt for the evening, scarf for the breeze, light raincoat, sweater for those who are sensitive to cold. For the reef, equipment for snorkeling, water shoes or rubber soled shoes.
In summer (December to February): tropics-friendly, loose fitting clothing, a light sweatshirt for the evening, light raincoat or umbrella.