subtropical high pressure center begins to migrate southward and low pressure
troughs begin to impact lower latitudes (Ely 1997).
The greatest climatic influence of North Pacific tropical storms is in Arizona,
New Mexico, southern California, and southern Utah, as seen in the late
summer/early fall average precipitation totals for these regions (Table 3).
Tropical storms are areally extensive and have high rainfall intensities, so both
large and small watersheds are prone to flooding from these events.
North Pacific High
a. During the winter months when atmospheric circulation pat-
terns inhibit the influx of tropical moisture into the Southwest.
b. During the summer months when atmospheric circulation
patterns promote the influx of tropical moisture into the
Figure 6. Positions of the North Pacific High and Bermuda High.