Science: Capricious Carol

One of the trickiest jobs in meteorology is predicting the path of a hurricane. As hurricanes drift northward, they become entangled in the “planetary wind,” the broad, strong current of air that whistles around the earth in north temperate latitudes at heights between 10,000 and 40,000 ft. The planetary wind’s general flow is toward the east, so when it captures a hurricane off the U.S. east coast, it generally pushes the spinner out over the Atlantic. But, as many a meteorologist has discovered to his grief, the wind is not constant in direction; it whips from side to side in waves like a shaken rope, carrying hurricanes with it.

Pacific Wave. Hurricane Carol, which smashed, tangled and flooded New England last week, started her career as a run-of-the-mill hurricane, perhaps a little lazier than most. On Monday morning, she was dawdling along off South Carolina, watched by airplanes and Weather Bureau radar and spinning northward at only four miles per hour. By Monday afternoon, Carol was captured by the planetary wind. It picked up her whirling mass and carried it north northeastward at 18 to 20 m.p.h. The weathermen, studying their charts, expected her to veer more sharply to the east and pass harmlessly east of Nantucket.

Then came the meteorological kink that turned humdrum Carol into a raging hazard by leading her toward shore. It was a deep wave in the planetary wind, part of a disturbance that had been detected while still over the Pacific more than a week before. By 3 a.m. Tuesday morning, the wind was headed toward the north, carrying Carol at 35 to 40 m.p.h. toward Long Island. Warnings went out at once, but most people along the endangered coast had gone to bed unworried, confident that Carol would pass them by. Instead, she churned destructively across southeastern New England, destroying, among many other things, the steeple of Boston’s famous old North Church.

High Water. As hurricanes go, Carol was not unusually violent. Much of her damage, aside from the steeple, toppled trees and tangled wires, was caused by storm tides. A hurricane has several devices for raising the water level. In the “eye of the storm,” the center of the spinning doughnut, barometric pressure is abnormally low. So the sea is sucked upward, sometimes as much as four feet. In Carol’s case this effect was minor. The pressure in her center probably did not fall below 28.4 inches (of mercury) and so could not have lifted the sea level much more than two feet.

But the furious winds spiraling toward Carol’s center piled up the water in a wave-topped mound that swept with the hurricane toward the helpless coast. When it finally hit, the wind-driven water had nowhere to go. Dammed up by wind pressure, it submerged the breakwaters, sandspits and islands, covering them deeply enough to allow the great waves to ride into harbors and bays.