In Micronesia there are two seasons: a wet summer and a dryer winter.
Temperatures rarely go above 90° F. and rarely below 70° F. Rainfall in
the Marianas averages approximately 85 inches per year, in the Palaus
approximately 150 inches, in the Carolines it ranges from 129 to 185
inches, and in the Marshalls it goes up to 160 inches. The humidity is
excessive, the average annual mean of relative humidity for selected
islands in Micronesia being between 82 and 86 percent. The relative
humidity is lower in the western Carolines and the Palaus, than in other
parts of Micronesia.
The Mariana Islands lie between the area of the Asiatic monsoon and the
belt of the northeast trade winds. At Saipan from November until March
or April, winds usually are easterly or northeasterly and are strong and
steady since the northeast trades and the winter monsoon reinforce each
other. In April and May the directions of the winds shift toward the
southeast, and they become weaker and more variable. In this period
there may be some easterly winds in addition to the predominating
southeasterly winds. Detailed information is not available on the winds
which occur in the Marianas north of Saipan, but at Pagan easterly winds
probably prevail from May to July and westerly winds prevail in the
remainder of the year. The Carolines lie in the belt of alternating
northeast trade winds and southwest monsoons. The northeast trades begin
in October and prevail until May or June. The southwest monsoon occurs
from May to October and may be felt as far east as Truk. To the
eastward, the winds of the summer are usually light and variable. In the
Marshall Islands, the northeast trade winds predominate from about
December to April, especially in the northern part of the Marshalls. In
summer, winds are variable and weak; periods of calm may occur. Typhoons
and squalls occur most frequently in the spring and summer in
Micronesia. Some of the severe typhoons are known to engulf entire
islands, as did the one at Woleai in 1907.