As our tropical summer progresses, the temperature of the ocean’s surface waters increases by about 3ºF.  Warmer ocean temperatures help provide the energy to start tropical cyclones, so the chance of a cyclone here is greatest between November and April. 

Cyclones have hit American Samoa at intervals of 1-13 years during the past 30 years: 1981 (Esau), 1987 (Tusi), 1990 (Ofa), 1991 (Val), 2004 (Heta) and 2005 (Olaf). Their severity varied—Tusi was particularly damaging to Manu’a, the back-to-back cyclones Ofa and Val hit Tutuila hard, Heta’s overall impact was moderate, and Olaf slammed into Manu’a with Category-5 force.

A world map of cyclone tracks helps put some perspective on American Samoa’s susceptibility to tropical cyclones. This map shows the tracks of all cyclones greater than 74 mph during the 10-year period 1994-2003. It shows that cyclones are generated primarily in two bands that lie north and south of the earth’s equator at latitudes of about 10-30º.

American Samoa lies near the edge of the cyclone band in the southern hemisphere where cyclone activity begins to fade.

Cyclones are a regular but erratic feature of the environment in our part of the world, so it is likely that native species here are able to cope with cyclone impacts and recover, given enough time and assuming that their recovery is not jeopardized by human-related conditions such as habitat loss due to urbanization, competition by invasive alien species, or changing environmental conditions due to global warming.