In American Samoa, an archipelago in the Pacific Ocean located south of the equator, the climate is hot, humid and rainy throughout the year, with a maximum in rainfall from December to March, and a relative minimum from June to September.
Temperatures are stable, with little variations between the hottest period (December to April), when highs are about 31 °C (88 °F), and the coolest period (June to August) when they are around 29 °C (84 °F). Night temperatures are almost always above 20 °C (68 °F). The south-east trade winds blow steadily throughout the year, especially from May to October, and are stronger during the day, making the heat more bearable.
Here are the average temperatures of Pago Pago, the capital, located on the main island, Tutuila.
Pago Pago - Average temperatures
Min (°C)252525252525252525252525
Max (°C)313131313029292930303031
Min (°F)777777777777777777777777
Max (°F)888888888684848486868688

The rains fall in the form of downpour or thunderstorm, and usually they are intense but they don't last long, so that the sun shines quite frequently and regularly, even in the rainiest months. From December to March, however, sometimes the rains may last for the whole day.
Rainfall is enhanced by the slopes that are found on the volcanic islands (Tutuila, Ta'u, Ofu and Olosega), which, therefore, are wetter, while the small islands and the flat atolls (Aunu'u, Swains and Rose), receive less rainfall, about 2,500 millimetres (100 inches) per year. On the volcanic islands, the amount of rainfall varies depending on slope exposure, so that it goes from about 3,000 mm (120 in) per year along the sheltered coasts, to 4,000 mm (160 in) per year on the coasts exposed to the trade winds; in hilly and mountainous areas it can even exceed 5,000 mm (200 in) per year.
In Pago Pago, located on Tutuila Island, 3,100 mm (122 in) of rain fall per year, with a maximum of around 370 mm (14.5 in) in December and January, and a minimum of 150/165 mm (5.9/6.3 in) between June and August. Here is the average precipitation.
Pago Pago - Average precipitation

Pago Pago

The sea in American Samoa is warm enough to swim in all year round, as you can see in the following table.
Pago Pago - Sea temperature
Temp (°C)292929292928282727282829
Temp (°F)848484848482828181828284

Tropical cyclones

American Samoa is exposed to the tropical cyclones of the South Pacific. Cyclones are usually formed from November to mid-May, though they are most likely from late December to early April. Outside of this period there has been cyclone Keli, in June 1997.

When to go

The best time to travel to American Samoa runs from June to September, in fact it is the least hot and the least rainy; anyway, even in this period, downpours and thunderstorms must be put into account.

What to pack

All year round, tropics-friendly, loose fitting clothing, a sun hat, a scarf for the breeze, a light sweatshirt for the evening, a light raincoat or umbrella.