88 
PACIFIC SCIENCE, VoI. II, April, 1948 
WIND DIRECTION 
The diurnal wind patterns for Oahu and 
Lanai are shown in simplified form geograph¬ 
ically in Figures 1 and 2. The full arrows show 
the normal daytime surface wind direction, and 
the dotted arrows the night winds. The regime 
at Waianae is from non-instrumental observa¬ 
tions only, but the wind changes shown on the 
map for other places are all established by re¬ 
cording wind vanes. 
The locations of good records of wind direc¬ 
tion are unfortunately distributed. A plethora 
of records exists in the Honolulu-Pearl Harbor 
area, though space does not allow all locations 
to be shown on the map of Figure 1. The data 
clearly establish the fact that there is usually 
no diurnal change in wind direction in the 
Honolulu area. This is true also at Aiea and 
Pearl Harbor. Yet only a short distance away at 
Waipahu a northwest night wind clearly shows 
up as the usual thing. 
All stations in the southern part of Oahu have 
a southerly afternoon sea breeze when the large- 
scale pressure gradient is weak and wind speeds 
low. These conditions characterize what is 
locally called "kona weather” on Oahu, when a 
general tendency for light southerly wind per¬ 
sists. 
Kaneohe, on the windward side of Oahu, 
shows no diurnal change in wind direction. 
Wheeler Field has the most variable wind, but 
during the day it is usually northeasterly, and 
in the night, northwesterly, north, or sometimes 
southerly. Waianae has a very definite afternoon 
sea breeze sufficiently strong on most days to 
give a westerly onshore wind, in direct opposi¬ 
tion to the tendency for a trade wind. 
It appears that sea-valley and land-mountain 
winds affect the wind direction over most of the 
westerly third of Oahu. Complete reversal of 
wind direction occurs only on the protected lee 
coast which lies down-trade wind of both the 
two mountain ranges. A nocturnal land-moun¬ 
tain wind prevails both at Waipahu and Waia- 
lua. 
A definite sea-breeze front can be found even 
on the small island of Lanai nearly every sum¬ 
mer day. Owing to the low mountain range and 
the generally dry weather, little vegetation 
grows on the lower parts of Lanai. The leeward 
plateau is nearly completely planted to pine¬ 
apple. This gives rise to strong surface heating 
and results in a well-marked sea-breeze regime. 
The map in Figure 2 shows the daytime wind 
directions and the mean position of a standing 
sea-breeze front. Directly above this front is a 
daytime cloud which can be seen on many an 
afternoon, its position moving a little from day 
to day depending on the strength of the sea 
breeze. This cloud is certainly the result of ris¬ 
ing air above the place where the sea and trade 
winds meet. A similar cloud line above the 
meeting place of sea and trade winds is charac¬ 
teristic of West Molokai. 
The diurnal rainfall regime directly related 
to wind patterns is very clear on the big island 
of Hawaii. Along the Hamakua coast of the 
windward or northeast side of the island, there 
is a definite mountain wind at night from the 
west, and in early morning a small cloud bank 
parallels the coast just offshore. The writer has 
noted the sea breeze begin at 1100 at the eleva¬ 
tion of 4,000 feet near Umikoa, and with this 
wind clouds blow in from the coast and rain 
begins about noon. The rain or drizzle ends in 
the late afternoon and it clears up about night¬ 
fall, remaining clear at Umikoa all night. The 
same phenomenon was noted by Dutton (1883) 
in the Kona districts of Hawaii. 
SURFACE WIND SPEEDS 
Average diurnal curves of wind speed for 
various stations are presented in Figure 4. 
Kaneohe Naval Air Station is located on a pen¬ 
insula projecting windward from the island 
mass, and approximately represents conditions 
over the open ocean to the windward of the 
islands. It is apparent that all stations show a 
maximum wind speed in the afternoon, but the 
island stations show slightly lower maximum 
