rangle) and Gulf Shores (Pensacola quadrangle) the highest amounts of monthly 

 rainfall occur in September (Table 32), with respective amounts of 21.1 cm 

 (8.30 inches) and 21.9 cm (8.61 inches). 



Rainfall in October averages the lowest for the year in coastal Alabama, 

 ranging from 9.4 cm (3.70 inches) at Gulf Shores to 7.9 cm (3.12 inches) at 

 Bay Minette (Bay Minette quadrangle). The lowest monthly average rainfall in 

 coastal Alabama occurs at Ft. Morgan during November. 



During winter months frontal systems and on-shore horizontal convergence 

 produce much of the precipitation in coastal Alabama. Snow (which averages 

 0.2 inches/yr), hail, and sleet are rare. Most of the rainfall occurs in 

 showers and long periods of heavy rainfall are rare. Monthly rainfall during 

 December, January, and February averages about 74 cm (29 inches)/month. 



Cloud Cover, Fog, and Relative Humidity 



Cloud cover in the vicinity of Mobile has an annual value of about 6/10 

 (60 percent of total sky area covered in daylight periods). In general, 

 cloud cover tends to be highest in winter and summer and lowest in spring and 

 fall. October has the minimum mean cloud cover with just over 4/10, while 

 January and July have maximum means of almost 7/10. Summer cloudiness is 

 mainly convective cumulus or high thin clouds, while winter cloudiness is the 

 result of frontal systems associated with extratropical cyclones and may 

 produce gray, overcast days (0'Neil and Mettee 1982). 



Fog is the main visibility inhibitor in coastal Alabama, occurring from 

 November through May. Winter fogs are fairly frequent and generally produce 

 the lowest visibilities of the year, 0.4 km (0.25 mi) (0'Neil and Mettee 

 1982). 



Because of the availability of water vapor from the Gulf surface, high 

 humidities prevail throughout the year with little seasonal variation. 

 Annual mean relative humidity at Mobile varies from 56% to 87% according to 

 the time of day, with highest readings at 6 a.m. E.S.T. Annual average 

 humidity is approximately 74% (National Climate Center 1980). 



Winds 



The prevailing surface winds for the coastal Alabama area are southerly 

 for March through July, easterly for August and September, and northerly for 

 the remaining months. The average annual wind velocity in coastal Alabama is 

 13.3 kmph (8.3 mph) (Chermock 1974). The Bermuda High is the most permanent 

 feature affecting the general circulation. During the spring, this sub- 

 tropical anticyclone intensifies and extends its western boundaries over the 

 Gulf region. This produces periods of prolonged light winds from a south to 

 southeasterly direction. The greatest (attained) winds occur from May 

 through November with passing hurricanes. The highest recorded wind speed in 

 the study area was 233 kmph (145 mph) on Dauphin Island during Hurricane 

 Fredric in September 1979 (Corps of Engineers 1981). The Bermuda High begins 

 to weaken in autumn and move slightly southeastward. This, along with the 

 southern movement of the equatorial trough, permits the continental pressure 



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