197 



near 35.00 per mil (Figure li-A and B) . Waters with the steepest salinity- 

 gradient were within 110 km of the shore, and surface waters having salinities 

 of 33.00 per mil, or less, extended to 210 km from shore (Figure ^t-A) . The 

 typically steep salinity gradients are noted from the curve in Figure hB. 



The loss of heat in the surface waters to the hurricane atmosphere 

 lowered the water temperatures, forming the inversions, and, because of the 

 brackish layer, the lowered temperatures did not result in a density instability 

 in the water. Prom climatologic records and previous data collected during 

 research cruises in the northwest Gulf, it is known that changes in water 

 temperatures in September and October are negligible . This has been sub- 

 stantiated by applying the techniques presented by Laevastu (1960) to the 

 factors influencing heating and cooling of surface waters. Furthermore, a 

 careful examination of the 91 bathythermograms taken on the October k-9 

 cruise showed no indication of heating, or cooling, of the surface waters. 



In the weeks following the occurrence of hurricane Carla, winds over the 

 waters of the northwest Gulf blew at low velocities, and there were several 

 successive days of light and variable airs. The wind directions were, as 

 normal, from the southeast. However, the low velocities produced wind- 

 drift currents of little consequence in re-establishing normal temperature 

 distribution. Isosteric surfaces, computed from data gathered on October ^-9, 

 were essentially flat. Therefore, no significant density currents were 

 present. 



With these considerations in mind, it was concluded that the water- 

 temperature structure of the northwest Gulf retained, for at least the suc- 

 ceeding h weeks, the dominant characteristics formed during hurricane Carla. 

 The inversions which were measured during October k-9 were believed little 

 modified from the configuration immediately following the hurricane. 



To the southeast of Galveston, where the vertical distribution of salinity 

 was nearly isohaline, the heat loss from the surface caused instability in 

 the upper layers. The consequent convective stirring produced an isothermal 

 layer which extended to depths of 60 meters (Figure 2) . 



THE TEMPERATURE DISTRIBUTION 



The distribution of surface water temperatures in the early days of 

 October reflected the influence of Carla (Figure 5). Warmer water was 

 centered in the area where the hurricane deviated from its northwesterly 

 course, whereas colder water was situated near the outer boundaries of the 

 low-salinity layer and over that part of the' shallow shelf which was beneath 

 the track of the storm. 



At depths of 50 meters ( Figure 6), the main 'cells' of warm and cold 

 water were even more sharply defined. The effects of the temperature 

 inversions were noted where temperatures were slightly greater than 28.0°C, 

 which was just more than 0.5°C warmer than those at the immediately overlying 

 surface . Farther from shore and to the right of the hurricane track, the 



