90 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Figure 17. — Normal sea level pressure, October. 



high temperature of the Gulf of Mexico waters 

 compared to those of other water surfaces in the 

 same latitudes brings about such a great warming 

 and increase in the moisture content of the over- 

 lying air masses that weather patterns of the area 

 are markedly affected. (The mean annual sur- 

 face temperature of the Gulf is 78° F., while that 

 of a comparable region at the same latitude in 

 the western Atlantic is 76°, in the eastern Atlantic 

 73°, and in the eastern Pacific 68°). 



Typical features of the winter circulation are 

 shown in figure 19. Here the winds are more from 

 the easterly directions with fewer southerlies but 

 more northerlies. There are very few winds from 

 the west or the southwest. The sea surface tem- 

 perature pattern shows a variation from more 

 than 75° F. in the southeastern portion to less than 

 65° in the northwest. Southeasterly winds bring 

 warm, moist air from lower latitudes and carry it 

 from warmer toward colder water in the Gulf. 

 When this flow is slow and sustained, the cooling 



by the ocean surface leads to condensation and 

 fog and stratus formation in the northern Gulf. 



A discussion of the upper air circulation for the 

 Gulf and Caribbean area is given by Erna and 

 Rudolf Penndorf (1944). 



AVERAGE CONDITIONS 



Average sea-level atmospheric pressures in the 

 Gulf vary from 30.00 to 30.15 inches of mercury. 

 There a>"e wide deviations from these averages in 

 individual synoptic situations. Worthy of note 

 is the diurnal pressure variation with a lesser 

 early morning minimum followed by a greater 

 late morning maximum and evening minimum 

 and a lesser nocturnal maximum. 



The Atlas of Climatic Charts of the Oceans, 

 published by the United States Weather Bureau, 

 and the Pilot Chart of Central American Waters, 

 published by the Hydrographic Office of the 

 United States Navy, issued monthly, give further 

 information about the winds, pressures, tempera- 



