Hawaiian Rainfall Estimates^ — Stidd 
271 
based on the records from a group of gauges 
spaced along the coast at distances of 27 to 
37 miles from Hilo. The slopes behind these 
stations are convex to the trades, making the 
precise direction of the trades a more impor- 
tant factor than it is at Hilo. The convexity 
also has the effect of giving each station a 
slightly different exposure, with consequent 
loss in homogeneity. 
Smaller mean annual rainfall amounts in 
this area and greater inhomogeneity among 
stations suggest that there is more random- 
ness in the Hamakua index than in the Hilo 
index, and this randomness helps reduce the 
relationship of the index to the 700-millibar- 
height field. Comparison of Figure with 
Figure 1 shows that the relationship is reduced 
to a marked degree, the highest correlation 
coefficient between Hamakua rainfall and 
700-millibar heights being only 0.44. 
NAALEHU 
Figure 5c shows the winter monthly pattern 
for the Naalehu index. This is a much drier 
area, responding more to cyclonic activity and 
less to trade winds than does Hilo. It will be 
seen to be very similar to the pattern for dry 
areas on the Island of Oahu, a fact which 
helps establish the principle that stations hav- 
ing equal mean annual rainfalls respond alike 
to a given rainfall stimulus. 
The high positive center on this pattern is 
far to the north, presumably the more readily 
to allow the development of negative values 
in the immediate vicinity of the Islands. It is 
unfortunate that data from more southerly 
latitudes are not available. Experience with 
patterns of this sort in other areas indicates 
that the nearby negative center might well 
be greater in magnitude than the distant posi- 
tive center. In fact, it is evident in all the 
patterns that important information could be 
found in the area south of the Islands. 
WET INDEX 
Figure 6a shows the correlation field pat- 
tern associated with the monthly rainfall from 
Fig. 6. Correlation field patterns of 700-millibar 
height versus Oahu wet-index (average of five high- 
rainfall stations on Island of Oahu), a, Monthly 
amounts, winter, 102 cases; b, five-day amounts, winter, 
255 cases; c, monthly amounts, summer (May through 
October), 102 cases. 
