Hawaiian Climatology— L eopold and STIDD 
waii at all elevations, and in the high rainfall 
zone of east Maui at elevations of 3,000-4,000 
feet 
The northeast exposures of both east and west 
Maui and the high rainfall zone of eastern 
Hawaii show marked rainfall minima in June, 
October, and February. The same zones gen- 
erally show sharp maxima in August, December, 
and April. Yet leeward Hawaii and Maui, all 
of Oahu, and all of Kauai exhibit no such 
striking behavior. 
The 20-year period on which Ttillman based 
his mean rainfalls is sufficiently long to be con- 
sidered fairly representative. The curves for 
certain of his groups might not have contained 
enough stations of long record and thus the 
adjustment procedure may have significantly 
affected their representativeness. Yet the con- 
sistency of these variations between certain 
areas lends credence to them. 
An unpublished study by the authors ( Stidd 
and Leopold, MS.), using more recent data, 
reaches conclusions which are in agreement with 
Tiillman’s findings. This study discusses two 
individual components of Hawaiian rainfall and 
shows that their annual cycles are quite different. 
The cycle of cyclonic activity is shown to have a 
winter maximum and a summer minimum while 
the cycle of orographic activity is found to have 
a three-phase annual cycle with minima in June, 
October, and February. These minima corre- 
spond exactly to the minima of rainfall found 
by Tullman in the very wet regions of Maui 
and Hawaii. 
The study also shows that mean monthly rain- 
fall distributions have the same type of pattern 
as the mean annual distributions, the only 
fundamental differences being in spacing and 
values of the isohyets. A quantitative statement 
of these two variables is shown to define ade- 
quately the rainfall distribution and magnitude 
for any mean month. 
The study implies that the pattern of mean 
annual rainfall can, as an approximation, serve 
as the pattern for rainfall over any given period 
219 
of time, and quantitative daily forecasts of rain- 
fall based on this approximation are now being 
made. 
Because of the skewness of the frequency dis- 
tribution of monthly rainfall values, the arith- 
metic mean is a poor statistic to represent normal 
values of Hawaiian data. The occurrence of 
abnormally wet months causes the mean rain- 
fall values to be significantly greater than median 
values. Landsberg (MS.) showed that median 
monthly rainfall values for Hawaiian stations 
reach stability in a shorter period of record 
than do means. But he noted that for an island 
as a whole, "the pattern of ishoyetal maps . . . 
if medians are used, shows no material differ- 
ence in areal distribution compared to maps 
using mean-value isohyets. The difference is 
one of absolute values, not a shift in the location 
of drier or wetter areas.” 
The greatest monthly and annual values of 
precipitation are obviously in the mountain area. 
Annual means vary from 430 inches on Mount 
Waialeale to less than 10 inches on the lee side 
of Maui. Studying the Honolulu area, Voor- 
hees (1928) found the correlation coefficient 
between mean annual rainfall values and station 
elevation to be only +.21; correlating annual 
mean with distance from the mountain crest 
gave a value of — .81. The maximum rainfall 
area in the Koolau Range on Oahu, average 
elevation 2,000 feet, lies about a mile leeward 
of the mountain Crestline. The Koolau Range 
is long and narrow and is oriented perpendicu- 
larly to the trade wind. 
The essentially conical-shaped mountain 
ranges of central Kauai and west Maui reach 
maximum elevations of about 5,000 feet. In 
both instances the maximum rainfall zones coin- 
cide with the maximum elevations. Yet on the 
higher ( 10, 000-14, 000-foot) conical mountains 
of Haleakala (east Maui), and of Mauna Loa 
and Mauna Kea ( Hawaii ) , the zone of greatest 
annual rainfall is on the windward side at ele- 
vations of about 3,000 feet, a fact noted by both 
the Territorial Planning Board Report (1939) 
and Jones (1942). Leopold (MS.) attributes 
