Diurnal Weather Patterns— LEOPOLD 
83 
strength of the easterly circulation around the 
Pacific high-pressure cell increases. Pressure 
troughs in this system of easterly winds also 
move in the direction of the wind, in this case 
from the east. These disturbances, called "east¬ 
erly waves,” provide, in summer, decks of high 
clouds as well as an increase in height and size 
of the normal fair-weather low clouds of the 
ocean. 
The importance of convective rain in the Ter¬ 
ritory has not been sufficiently emphasized. 
Rain or showers from cumulus or cauliflower 
clouds are often seen over the open ocean or 
over the lower and drier portions of the Ha¬ 
waiian Islands, particularly in the afternoon. 
Though well-developed thunderstorms are 
rare in the area, convective clouds built up suf¬ 
ficiently to yield rain are experienced during 
periods when the temperature inversion aloft 
becomes weak or disappears. The stability of 
the layer through the temperature inversion and 
the dryness of the air above the inversion 
ordinarily limit the height of development of 
cumulus clouds. 
Convective storms are sufficiently important 
to bear a local name, "naulu,” used on the 
islands of Maui, Lanai, and Molokai. It refers 
to a type of rain which occurs primarily in the 
afternoon, and which is characterized by short 
duration and high intensity. 
Fig. 2. Map of Lanai showing stations and wind directions. 
