84 
PACIFIC SCIENCE, Vol. XV, January 1961 
TABLE 1 
Climate of Marcus Island 
(The data are the averages obtained during 1952—4. Maximum and minimum values 
are the extreme ones noted during the four years. ) 
TEMPERATURE 
(°c.) 
MEAN 
RELATIVE 
HUMIDITY 
(%) 
WIND VELOCITY 
(m/sec) 
RAINFALL 
(mm.) 
Max. 
Mean 
Min. 
Max. 
Mean 
Total 
Max/hr 
January 
29.7 
22.4 
17.2 
72 
18.3 
7.6 
66.9 
28.5 
February 
28.5 
22.4 
16.3 
75 
18.1 
7.5 
53.5 
25.7 
March 
29.9 
23.0 
18.0 
76 
18.4 
7.8 
39.5 
10.9 
April 
31.9 
24.8 
18.4 
78 
17.6 
8.1 
37.8 
8.7 
May 
333 
26.3 
19.8 
78 
13.2 
5.7 
48.7 
15.9 
June 
33.8 
28.1 
23.1 
75 
12.4 
4.5 
43.0 
23.0 
July 
35.3 
273 
22.8 
78 
164 
6.0 
252.8 
59.2 
August 
33.7 
27.3 
21.8 
79 
15.6 
6.4 
189-1 
23.9 
September 
35.3 
27.9 
22.8 
76 
16.5 
73 
82.4 
31.0 
October 
33.5 
26.8 
21.9 
78 
18.9 
7.1 
117.8 
28.6 
November 
34.2 
26.0 
22.0 
77 
18.5 
7.1 
45.7 
12.3 
December 
31.6 
23.5 
18.5 
73 
21.6 
8.6 
66.1 
16.5 
Warmth Index, W — 245-8° C. Humidity Index, K = 5.4. 
it is suggested that Marcus has a relatively dry 
climate in spite of its oceanic position. Actually, 
it occupies an intermediate position between 
Aw and Bs of Koppen’s climate formula, al- 
though the differentiation of seasons is relatively 
less conspicuous. According to the climate clas- 
sification by Kira (1953), who established an 
excellent climate system based upon two very 
simple indices, warmth and humidity, 3 the is- 
land lies at the cool-arid corner of his type B (! 
( tropical semiarid climate ) . From the climo- 
graphs and hithergraphs shown in Figure 1 1 , 4 
together with those of Chichijima (Bonin Is.), 
Yap, and Honolulu, the annual cycle can be 
roughly divided into two seasons, namely, Octo- 
ber to April, which is dry, cool, and windy; and 
May to September, which shows the opposite 
3 Warmth Index: W = T (t-5), where t = mean 
temperature of each month; i = number of months 
when t>5. Humidity Index: K = 2P/(W+ 140), 
where P = annual rainfall, W = Warmth Index. 
1 In the hithergraph, high rainfall in July is mainly 
caused by an abnormally rainy weather in 1953 
(500.2 mm.). In other years, 76.8 (1951), 177.1 
(1952), 144.7 (1953), and 1893 0954), respec- 
tively. 
trends. Bryan also reported the danger of land- 
ing during October to April, because in that 
season the waves beat violently upon the reefs 
and shores. This was also confirmed in my trip 
by the staff of the weather station. As the is- 
land is located in the western part of the north- 
east trade-winds belt, the prevailing winds are 
from the east, but certain northern trends mingle 
during October to April Furthermore, the in- 
fluence of typhoons, which frequently visit in 
September and October, must not be overlooked. 
For instance, the island was completely washed 
by violent waves from the south to the north- 
west and eastern shores, when typhoon Sara 
passed over the island in October, 1951. Max- 
imum wind speed was 40.5 m/s; maximal in- 
stantaneous speed, 50.9 m/s; rainfall, 154.9 
mm. (For the effects of typhoons, see also the 
Appendix. ) 
The climatic features mentioned above may 
be well explained by the location and topog- 
raphy of the island. Gressitt (1954) mentioned 
that there was occasionally found a dry local 
climate within the generally wet, oceanic cli- 
mate of Micronesia, especially in low islands 
