In Guam, an island administered by the United States, which is located in the western Pacific Ocean between the equator and the tropic of Cancer, and geographically is part of Micronesia, the climate is tropical, hot and humid all year round, with temperatures around 30/32 °C (86/90 °F) during the day, and 24/25 °C (75/77 °F) at night.
Here are the average temperatures of Tamuning.
Tamuning - Average temperatures
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)242424252525252525252525
Max (°C)303030313131313131313030
Min (°F)757575777777777777777777
Max (°F)868686888888888888888686

The rainfall is abundant, above 2,000 millimetres (80 inches) per year; the rainiest period is from July to November, the driest is from January to April, in which, however, there is a moderate amount of showers and thunderstorms. Here is the average precipitation.
Tamuning - Average precipitation
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec.(mm)1159065851251602653653403102151402275
Prec.(in)4.53.52.63.34.96.310.414.413.412.28.55.589.6
Days191617171922252524252322254

The amount of sunshine in Guam is never excellent, though it is acceptable or good from January to June; from July to December, during the wettest period, it is quite scarce.
Tamuning - Sunshine
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Hours677776554445

Guam

For swimming, the sea is warm enough all year round, as can be seen in the following table.
Guam - Sea temperature
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Temp (°C)282828282929292929292928
Temp (°F)828282828484848484848482

Tropical cyclones



The island lies in the path of typhoons, the tropical cyclones of Southeast Asia and the Philippine Sea. Typhoons can cause more or less serious damage, bringing heavy rains and strong winds, and normally occur from May to December, though they are more frequent from August to November; sometimes, however, they have passed over the island outside of this period, as happened with Roy (January 1988), Isa (April 1997), and Kong-rey (not strong, April 2007).

When to go



The best time to travel to Guam is from February to April, being the least rainy of the year, and (normally) outside of the typhoon season.

What to pack



All year round, light clothes, of natural fibres, sun hat, a scarf for the breeze, a light sweatshirt for the evening; light raincoat or umbrella.
For the reef, equipment for snorkeling, water shoes or rubber soled shoes.