Diurnal Weather Patterns on Oahu and Lanai, Hawaii 
Luna B. Leopold 1 
INTRODUCTION 
Weather forecasting in the Pacific area 
has been predominantly aimed at serving air¬ 
plane operations. On the other hand, little or 
no developmental work has been done to pro¬ 
vide bases for weather forecasts for agriculture. 
In Hawaii the two largest industries are agri¬ 
cultural-—-the growing of sugar cane and pine¬ 
apples. Techniques and organization to provide 
both long- and short-range forecasts would be 
of considerable aid to these industries. 
Though a long-continued interest in weather 
on the part of agriculturists in Hawaii is shown 
by a large number of rain gages and tempera¬ 
ture measurements, detailed analyses involving 
additional critical data are required to give 
accurate pictures of the variations of meteoro¬ 
logical elements over the diverse topographic 
areas of the islands. A better over-all descrip¬ 
tion of these factors is an early step in the 
development of a sound basis for local fore¬ 
casting. 
Hawaii, lying in the trade-wind zone, experi¬ 
ences relatively small, day-to-day variations in 
weather when compared with a continental 
locality in the belt of westerlies. Yet great dif¬ 
ferences in ecologic habitats are found within 
very short distances. Day-to-day synoptic 
changes are subtle and difficult to follow, owing 
to the wide expanses of ocean where no upper 
air data are obtainable. Particularly in such cir¬ 
cumstances, the study of diurnal fluctuations may 
contribute to a better understanding of the man¬ 
ner in which the great local differences originate. 
Figures 1 and 2 show the location of stations 
on Oahu and Lanai which are discussed in this 
paper. The profiles drawn in the direction of 
^Meteorologist, Pineapple Research Institute of Ha¬ 
waii. Manuscript received September 11, 1947. 
the prevailing trade wind, ENE-WSW, provide 
some picture of the topography. On Oahu, the 
two ranges of mountains are oriented nearly 
perpendicular to the trades, and, therefore, pro¬ 
vide barriers causing large differences in oro¬ 
graphic rainfall. These have been discussed in 
connection with the mean annual isohyets of 
Voorhees (1929) and by Nakamura (1933), 
Wentworth (1946), and others. 
Acknowledgments: The writer acknowledges 
with thanks the help of M. H. Halstead and 
Gretchen Hastings, who assisted with the tabu¬ 
lation. C. K. Stidd contributed in helping with 
the drafting of the figures. Charles M. Woffin- 
den and the staff of the U. S. Weather Bureau 
co-operated by making the special radiosonde 
ascents. 
DIURNAL RAINFALL PATTERNS 
As described previously, rainfall in Hawaii 
results primarily from orographic effects on the 
trade winds, from frontal passages, and from 
easterly waves. Most "kona” storms are actually 
related to frontal passages. 
Kona weather is a local term which often is 
erroneously used to imply a condition of south 
wind. A better translation for the word kona is 
"leeward,” and in terms of weather, it implies 
a cessation of the normal northeasterly trade 
wind. This ordinarily causes a strengthening of 
onshore sea breezes. 
On the southern coast of Oahu, for example, 
northeasterly winds blow more or less continu¬ 
ally during ordinary trade-wind weather in spite 
of a tendency for an onshore sea breeze to de¬ 
velop in the afternoon. When the trade wind 
decreases, the sea breeze asserts itself. 
On even more sheltered leeward coasts an 
afternoon sea breeze is the rule, and a decrease 
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