Table 1.2. Representative Temperatures at Galveston, 1951-1980. 
Measurement 
Date 
Temperature 
CF) 
Average monthly low temperature 
February 
49 
Average monthly low temperature 
July 
78 
Average monthly high temperature 
February 
62 
Average monthly high temperature 
July 
88 
Source: Compiled from Larkin and Bomar, 1983 (8); Riggio and others, 1987 (9), and Schexnayder, 1987 
( 10 ). 
According to a classification developed principally on annual rainfall, the study area lies in an 
"Upper Coast" climate (9). Based on 1951-1980 records for this climatic division, the average annual 
precipitation at Galveston is about 44 inches. Most precipitation at this location occurs in early fall 
and late spring and coincides with the passage of frontal systems. Average annual precipitation is 
nearly balanced by the average annual gross lake evaporation rate, which is 45 inches. Mean annual 
sunshine, expressed as a percent of possible sunshine, is about 60 percent. 
Representative winter and summer temperatures at Galveston are shown in Table 2 (8). Because 
the Gulf of Mexico moderates the temperature in all seasons, the temperature inland has greater 
extremes. For example, the average monthly low temperature in February in Houston is nearly 44 °F 
(49 T in Galveston); the average monthly high temperature in July in Houston approaches 94 °F (88 °F 
in Galveston). Average winters in Galveston have only four days with a temperature below freezing 
and summers have an average of 13 days above 90 *F. The lowest recorded temperature is 8 °F in 1899; 
the highest temperature is 101 °F in 1932. At the Galveston Airport, mean relative humidity is 83 
percent at 6 a.m. and about 90 percent at 6 p.m. (10). Winters are mild, and summers are warm and 
humid; there is less daily temperature variation in summer. The bay area averages 335 growing days 
for local agriculture. 
The predominant winds for the year blow from the southeast (8). However, wind patterns for the 
summer are very different from winds patterns for the winter (Figure 6). In June through August, 
winds have mainly southern and eastern components. From December through February, north 
winds blowing in excess of 10 knots dominate, and alternate with lighter south winds. During "blue 
northers," winds up to 40 knots increase wave height, push several feet of water out of the bays, and 
tilt the level of the bay surface. Then oyster reefs commonly stand well above the water surface. 
The Texas climate has two phenomena that greatly skew average and mean climatic data— 
droughts and hurricanes. A serious drought has harmed some region in Texas each decade of the 20th 
Century: During 1950-1956 a major drought plagued every sector of Texas. A drought in the river 
basins supplying fresh water to the Galveston Bay System is potentially more devastating than 
drought within the bay system. The Texas Water Commission made a special study of droughts (9) 
between 1931 and 1985 to plan water needs better. A map (Figure 7) of the frequency of occurrence 
of six-month drought in Texas, 1931-1985, shows the basins to be less affected than most of Texas. 
However, 22 such droughts affected the West Fork of the Trinity River. If severe to extreme droughts 
are considered, only six to eight severe droughts occurred here, compared with more than 12 
droughts elsewhere (including Laguna Madre). 
Tropical storms or hurricanes strike the Texas coastline with a frequency of 0.67 storms per year 
(11). The amount of geomorphic adjustment or damage caused by these storms depends upon the 
approach speed, wind velocity, barometric pressure at the storm's eye, storm surge height, wave 
height, direction of approach to the coast, and total rainfall. Recorded maxima of these parameters 
are, respectively, 17 mph for an unnamed storm at Port O'Connor in 1929; 140 mph for Hurricane 
Beulah at Brownsville in 1967; 27.49 inches (lowest) at Port O'Connor for Hurricane Carla in 1961; 22 
12 
