193 

 INTRODUCTION 



Hurricane Carla entered the Gulf of Mexico through the Yucatan Straits 

 on September 7, I961. From there it traveled in a northwesterly direction 

 and grew to be one of the five severest hurricanes to invade the Gulf since 

 1837 • By September 10, as it approached the Texas Coast (Figure 1,), pres- 

 sures in the center were 931.2 mb, and winds of 130 knots whirled around the 

 eye. Because of the early and continuous advisories issued by the U. S. 

 Weather Bureau, nearly 500,000 people evacuated the coastal regions. Thus, 

 despite the fury of the storm and the accompanying storm surges (a maximum 

 of 7 meters where the storm crossed the coast), few persons were injured. 



The energy exchange between the sea and the atmosphere is several orders 

 of magnitude greater during a hurricane than in less severe tropical cyclones. 

 Hurricanes provide, therefore, a unique 'laboratory' for investigations of 

 air-sea interaction. However, the taking of in situ measurements of water 

 temperature changes is virtually impossible. Aboard ship, nothing can be 

 done but to practice survival techniques, and even these are imsuccessful on 

 many occasions. Weather buoys have broken from their moorings, never again 

 to be seen, and towers have foundered. 



It was, therefore, a fortuitous set of circumstances by which changes 

 in the water temperature distribution affected by hurricane Carla were 

 'preserved' for investigation at a moire peaceful time. 



NORTHWEST GOLF WATERS IN THE FALL OF I96I 



Throughout the year a low-salinity layer of water lies along the coast 

 of the northwest Gulf. The variations in the salinity, width, and thickness 

 of the layer are dependent primarily upon the volume of river runoff coming 

 through the numerous estuaries and lagoons. Usually the surface salinity is 

 approximately 30.00 per mil close to the shore. A salinity of 36. 50 per mil 

 is normal at distances of 30 to 50 km from the coast. The water of 30.00 

 per mil may extend to depths of 20 to 30 meters, below which salinities of 

 36.00 per mil are encountered at ^K) to 50 meters. 



In September I96I, the brackish surface water lay in a bulge which 

 extended some 120 km from the coast between the Mexican border and Galveston, 

 Texas. It was over this bulge that hurricane Carla swept on September 10 

 and 11 ( Figure l) . 



A month later, between October 4-9, scientists cruised aboard the R/V 

 HIDALGO , of the ASM College of Texas, to investigate the distribution of 

 temperatures and salinity. Many of the traces from bathjrthermograph casts 

 revealed temperature inversions, with magnitudes as great as 2.5°C, extending 

 to depths of 83 meters ( Figure 2) . The inversions were all within the area 

 of the brackish bulge ( Figure 3). Salinities of 29.76 per mil were 

 encountered near shore, and salinities of 30.00 to 31-00 per mil were measured 

 though depths of kO meters. In most of this area, water of 36. 00 per mil lay 

 below 100 meters, although at 70 "to 80 meters the salinities were usually 



