Isaac's Storm - Erik Larson [9]
Soon, however, the sky filled with puffy clouds, Cumulus humilus, the pretty fair-weather cumulus of the finest summer days. As the wave advanced, these grew fatter and taller. High clouds arrived next, first icy cirrus, then a gray ceiling of cirrostratus. The skies got darker, the cloud ceiling lower. A fine drizzle began to fall. A squall line of thunderstorms followed, cousins of the great storms that just a few days earlier had driven the shopkeepers of Dakar to seek shelter. The storms brought thunder and lightning, but were nowhere near as intense as they had been over the West African bulge. They dropped the temperature at sea level to below 70 degrees. For anyone acclimated to the humid warmth of the tropics, suddenly the air was downright cold. It was jacket weather on Cape Verde.
The squalls passed. The sky cleared. The cycle began again.
WHEREVER THE AUGUST wave traveled, it dropped the pressure exerted by the atmosphere. At first the decline was slight, but soon warm air flowed upward through the thunderheads heating the air and reducing its weight, thereby reducing the pressure it exerted on the ocean surface. The heating produced a basin of low pressure that drew air, as wind, from surrounding regions of higher pressure. Meanwhile, ambient upper-level winds whisked away the air exiting from the top of the storm. The faster the upper air departed, the faster the lower air arrived. A few clouds became so immense they began to shape the behavior of the entire mass.
The storm could have continued growing, but conditions were not quite right. The air moving from its top had begun to descend, but in a form very different from when it first entered the storm. Stripped of its moisture, this descending air was cool and dry. Cataracts of spent air fell toward the sea beyond the boundaries of the storm, but the storm’s appetite had grown so large it now summoned this air as well. The cool air became caught—“entrained”—in the moist sea-level winds rushing toward the storm. As this dry air mixed with the moist, it banked the fires rising through the clouds above.
For the moment, the system stabilized.
IN GALVESTON, THE humidity was nearly one 100 percent. To move was to drip. It was too hot to put on a bathing suit. “Brown is the new color for bathing suits,” the Galveston News reported in the caption of a photograph showing the latest in coastal chic. “This one of a rich leaf brown mohair has yoke, collar and bands of white mohair striped with black braid.”
Mohair.
Every day an ad in the Galveston News for Dr. McLaughlin’s Electric Belt asked: “Weak Men—Are You Sick?”
MOST TROPICAL DISTURBANCES dissipated over the open sea. They collided with powerful winds from the west that dipped from the middle latitudes and blew the tops off their thunderheads. They encountered pools of cold water. They entrained so much dry air they lost their passion. Their pillars of smoke and light became mist. Most of the time.
Occasionally they became killers, although exactly why remained a mystery even at the end of the twentieth century. Satellites sharpened the ability of forecasters to monitor hurricane motion but could not capture the instant of transfiguration. No matter how closely meteorologists analyzed satellite biographies of hurricanes, they still could not isolate the exact coding that destined a particular easterly wave to a future of murder and mayhem. Satellites could document changes in temperature of a few thousandths of a degree and capture features as small as a foot wide or a few centimeters tall. “But suppose,” wrote Ernest Zebrowski Jr., in Perils of a Restless Planet, “that a tropical storm develops, and that we play back the data