Windswept_ The Story of Wind and Weather - Marq de Villiers [24]
More than a hundred such systems drift out of the Sahara into the ocean each year.
When they reach tropical waters, they either stall, or they don't. Again, if the conditions are right—the water temperature just right, the upper atmosphere still so no shear is found at the high altitudes to cut off their tops—the low-pressure systems they have become begin slowly to spin as the Coriolis force takes hold.
The Emi Koussi cell was one of these. In the ocean south of the Cape Verde Islands the Canary current had already reached 28.8° Celsius. The high-altitude winds were steady at low velocities. It was a formidable combination. The effect was like taking the lid off a pot of steaming water—moist air began to ascend rapidly, moisture and energy were dumped at high altitudes, surface winds rushed into the vacuum thus created and in turn forced the winds into a tighter circular motion.
By this time the National Hurricane Center in Miami had taken notice.
The cell was now formally a tropical depression, and as such it was assigned a number. It was the ninth of the season. Tropical Depression Nine, with sustained winds still under the tropical storm threshold of 39 miles an hour, was located 555 miles southwest of the Cape Verde Islands. It was September 2.
I
I was once pursued by a windstorm across the arid Great Karoo of South Africa. I'd been spending a few days with a friend at his aunt's house in the little town of De Aar—I mostly recall being stuffed by that hospitable woman with all the traditional delicacies of the Afrikaner heartland, grilled baby lamb, roast springbok, pan-nekoek and moskonfyt, babootie, and the rest—and we had headed back to Cape Town on Willie's knockabout motorcycle. The first we knew about the storm, the first inkling that something was amiss, was when our own dust overtook us; a following wind had gotten up, and it was strengthening fast. I looked over my shoulder and the horizon was already a luridly dirty purple lit up with sheets and jagged spears of lightning. For a moment I thought I saw a yellow-tinged funnel shape reaching toward the ground, and if it were true, that would mean really bad news. "Get on with it, Willie!" I said, and he opened the throttle and we made a run for it.
The machine juddered over the ruts. I could feel the storm behind me, chasing . . . This was stupid, I knew even then. It was just a storm, the basso rumbling that followed us just thunder, the flashing just lightning, the hail just ice, the wind just wind, and the massive clouds of debris—thorn bushes, small birds, dust and grit, tumble-weeds— was aimed at nothing at all. I knew that. I was no longer a child, to be battered by every passing gale. But phobias seldom pay court to rationality, and trump volition every time.
Wliy was the damn thing following me?
For three hours the storm nipped at our heels. The bike wasn't very good and the gravel road was very bad; we were making no better than 40 miles an hour, and the storm was keeping pace, traveling at furious speed across the veld. Even Willie, a structural engineer by training and temperament, felt its malice, or so I fancied. Finally, after hours of bone-jarring flight, the arrow-straight road veered left, and when we could see we were no longer in the direct path, we stopped the bike and watched the monster pass.
That the storm was moving was evident. We could see it coming after us, we could see it pass by, we could see it vanish over the horizon. So why, I wondered in later years, did no one figure out, in the centuries past, that weather traveled? The Tuareg in the desert could watch storms pass, mariners at sea could surely see how they moved. And yet, in two thousand years of musings about winds, by some of the brightest intellects in history, the notion that storms were self-contained "systems"