Annual March of Daily Mean Temperatures at Honolulu 
Harold S. Palmer 1 
The present paper attempts to answer 
objectively the recurring question as to when 
the warmest and coldest weather occurs at 
Honolulu. For basic data the "daily mean 
temperature,” which is the arithmetic mean 
between the maximum and minimum tem- 
peratures recorded during the 24-hour day, 
was chosen. It is usually reported to the near- 
est whole degree, since the temperatures used 
for its computation are not reported in frac- 
tions of a degree. If the arithmetic mean ends 
in five-tenths of a degree, it is arbitrarily 
rounded to the nearest even degree, whether 
this involves rounding up or rounding down. 
In 1931, Ml John F. Voorhees, then mete- 
orologist of the Honolulu office of the U. S. 
Weather Bureau, supplied me with averages 
of the daily mean temperatures for each of 
the 365 days of the year. These covered the 
4 1 -year period from 1890 to 1930, inclusive. 
I do not know where the instruments were 
located from 1890 through 1904. From 
1905 to 1922 the records were made on the 
Young Hotel Building, 121 feet above the 
ground, and since 1922 on the Federal Build- 
ing, 99 feet above the ground. The difference 
in stations is not significant for the present 
study since it compares the averages for eacn 
date of the year and does not compare data 
from earlier and later periods. Leap day has 
been omitted from consideration. 
Mr. Harry T. Tanaka, a student at the 
University of Hawaii, working on N. Y. A. 
funds, tabulated the daily means for the 10- 
year period from 1931 through 1940, and I 
have added the data for the 7 years from 
1941 through 1947, thus getting the average 
daily mean temperatures for each of the 365 
1 Department of Geology, University of Hawaii. 
Manuscript received May 27, 1949- 
dates for the 5 8-year period from 1890 
through 1947. The averages were calculated 
to tenths of a degree and are given in Table 1 
and are shown graphically in Figure 1. 
A study of the data for the 5 3 -year period 
from 1890 to 1942 was reported to the 
Hawaiian Academy of Science, in 1943 
(Palmer, Harold S., The Annual March of 
Daily Mean Temperature at Honolulu. [Ab- 
stract] Hawaii Acad. Set. , Proc. 1945: 3). 
For that study a number of ways of smooth 
ing and otherwise treating the raw data were 
tried. The method finally chosen as most sat- 
isfactory was that of 7-day progressive means, 
and is used in the present study. The method 
is this: the values for seven consecutive days 
are added, the sum is divided by seven, and 
the quotient is used for the middle, or fourth, 
day of the seven. The resulting 7-day pro- 
gressive means are given in Table 2 and are 
shown graphically in Figure 2. 
THE COLDEST DATE 
The data show that February 12, 13, and 
14 have the lowest smoothed temperatures, 
namely 70.9° F. It is reasonable to suppose 
that February 13 is the coldest of the three, 
and this is confirmed by the fact that it is 
the coldest date among the unsmoothed data. 
Calculation of the smoothed values to hun- 
dredths of a degree further confirms this 
choice since the values for February 12, 13, 
and 14 are 70.92°, 70.91°, and 70.93°, re- 
spectively. It must be admitted that working 
to hundredths of a degree is unwarranted 
since the raw data were taken only to the 
nearest whole degree; but the calculation is 
given for what it may be worth. 
A disagreement is found in the data for 
the 17 -year period, 1931-1947, similarly 
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