2 Winds Over the Harbors 
Typical Conditions 
The basic feature of the wind pattern for the harbors is a land-sea breeze 
regime caused primarily by differential heating of water and land. In 
summer, this pattern is characterized by onshore winds from west to 
southwest during the day, peaking at about 20 mph.' Onshore wind can 
persist throughout the night. From Figure 1 it can be seen that these onshore 
winds move along the wider axis of the outer harbor of both ports, i.e., from 
a westerly direction. Figure 2 shows onshore winds predominating from 
1-19 July 1988. The direction shown is the direction from which wind is 
blowing, measured clockwise from true north. The 22 June - 20 July 1988 
wind rose (Figure 3) illustrates this onshore predominance. Figure 3 shows a 
cumulative plot of measurements near Angel’s Gate indicating the predominant 
wind direction from 240-260 deg. Because wind measurements shown in 
Figures 2 and 3 were collected on the San Pedro breakwater, they are 
representative of winds over the harbors’ water surface. Typically the daily 
duration of onshore winds reduces as daily temperatures reduce in cooler 
seasons. The 16 October - 13 November 1985 wind rose (Figure 3) shows 
that even in fall/winter the onshore southwest winds are still an important 
component of the wind pattern. However, strong winds from the southeast 
and north-northwest, associated with approaching and passing frontal 
conditions, respectively, become important with regard to winter wind patterns 
and are the dominant winds in the October - November wind rose. Northwest 
winds are intensified for several days after passage of a front, with sustained 
winds of up to 25 mph being common. “Hurricane Gulch" is a commonly 
used term to describe the stronger westerly winds from Cabrillo to Seal 
Beach, due to the northwest winds whipping around Palos Verdes’. 
' A table of factors for converting non-SI units of measurement to SI units is presented on 
page vi. 
2 Personal Communication, August 1993, Jane Grandon, Civil Engineer, U.S. Army Engineer 
District, Los Angeles, Los Angeles, CA. 
Chapter 2 Winds Over the Harbors 
