First, when traveling to American Samoa, you need to realize you are of course traveling to a tropical island.  Expect heat, and expect rain... anytime of year.

 Unlike other larger islands (like the neighboring islands in western Samoa of Upolu and Savaii) the islands of American Samoa are quite small.  Thus, there is little difference in the leeward and wayward sides of the islands.  Or stated differently, there isn't a dry spot in the territory.

 Typically, the "rainy" season is defined as October through April.  However, there is really little difference in rainfall amounts between the rainy and dry seasons.  More importantly, however, most tourists will notice the rainy season (our Summer months) are much warmer than our dry season (our Winter months).  This is in part because of the slightly lower temperatures (highs during the winter months average around 83 degrees.  highs during the summer months average around 86 degrees).  But the primary cooling factor are the tradewinds which are more constant during the winter months.

 American Samoa could easily receive 20 inches of rain during a dry season month, yet only 8 inches of rain during a wet season month.  Usually, each wet season month we will receive 12 inches, while during a dry season, we will only receive 7 inches. Our hurricane season extends from November through April.  Hurricanes are very rare, but still possible, and travelers should plan accordingly.

 Although American Samoa doesn't have much of a tourism industry, the few hotels on-island are often overbooked during the months of June through August.  If you're planning a trip, either book a room early during these months, or plan for another month.