The new air world

by Willis L. Moore

Highs and Lows alternately drift across the continent in periods of about three days each. They are a part of the divine economy that provides for the seedtime and the harvest, for, as previously stated, the Lows draw the warm, vapor-bearing currents inland from the Gulf and the ocean and cause them to deposit their moisture far to the north and west. Four sevenths of all our storms come from the middle or the north plateau regions of the Rocky Mountains, or at least enter our field of observation from those regions, and pass from this arid or sub-arid section of the continent easterly over the Lakes and New England, producing but little rainfall. The greater part of the remaining three sevenths are first observed in the arid regions of our southwestern States; they always move northeastward and can be depended on to give bountiful rainfall so soon as or a little before they reach the Mississippi River. Some of them cross the Atlantic and affect the continent of Europe. [Charts 10] and [11] show the courses of storms in this country, and where they originate, or are first brought under the survey of our system of observation.

Chart 11.—Storm Tracks for February for Ten Years.

West Indian Hurricanes. A few of the most severe storms that touch any portion of our continent originate in the West Indies and travel in a northwesterly direction until they touch our Gulf or South Atlantic coast, when, passing from the influence of the northeast trade winds which carried them westward, they recurve and pass along our eastern coast, usually with their centers offshore and following the Gulf Stream. These violent atmospheric convulsions are usually detected in the process of formation through the effectiveness of the storm-warning service established by the writer during the Spanish-American War, under the direction of the President, for the purpose of giving warning to our fleet before the coming of a hurricane. The President realized the great part played by storms in many of the naval battles of the past, and it may be surmised that he was more afraid of a West Indian hurricane than he was of the Spanish Navy. But Cervera was beaten and the blockade was raised before the hurricanes of 1898 began.

Galveston Hurricane. The new Weather Service, with a cordon of stations down the Windward Islands and along the north coast of South America, surrounding our fleet, and inaugurated as a war measure, so demonstrated its value in locating and giving warning of the coming of a hurricane soon after the end of the war that Congress continued it as a permanent instrument of peace; and when the destructive Galveston Hurricane occurred in 1900 it detected the storm at its inception and so fully advised shipping of the storm’s movements that not a vessel was lost as the storm roared and gyrated across the Gulf of Mexico and crashed upon the Texas coast, destroying a large part of the city and drowning six thousand people.

The hurricane is simply a rapidly gyrating cyclone; it usually is only one to three hundred miles in diameter. The storm that destroyed Galveston moved across the Caribbean Sea at the rate of only about eight to ten miles an hour. It increased its rate as it moved northward, crossing the Gulf at about fifteen miles per hour. The speed of translation was so slow and the velocity of gyration so rapid that immense swells were propagated outward from the center of the storm; they reached the Texas coast some sixteen hours before the storm itself reached Galveston. As it moved northward to Iowa its velocity of translation increased and its rate of gyration decreased, so that it crossed the Lakes with both movements at about sixty miles per hour. At Galveston the anemometer blew to pieces after recording one hundred and thirty miles per hour.

Danger to Atlantic Coast Summer Resorts. The writer frequently has been asked as to the possibilities of a populous Atlantic coast resort being submerged by the waters driven inshore by a hurricane, or being lifted up in the center of the storm as the result of decreased air pressure inside the cyclonic whirl. The answer is that such a catastrophe is possible to any Atlantic coast city (more especially those south of Norfolk) that is not protected by a heavy breakwater of ten to twenty feet above sea level, and whose building foundations and walls are not of brick or concrete for at least ten feet above the water level. It would be necessary for a West Indian hurricane of unusual intensity—one similar to that which wrecked Galveston—to be considerably deflected westward out of its normal track in order to hit one of our coast cities north of Chesapeake Bay so that the center of the storm would pass over it, or near enough to cause destruction. In Galveston there was little damage to strongly constructed buildings of brick or stone.

The Breaking of Droughts. It is most important for the forecaster to know when and how droughts may be broken. He will observe that when the great cereal plains are famishing for moisture the Lows all originate on the middle or north Rocky Mountain plateau, in the region of Colorado or Montana, and that the drought continues until the Lows begin to form in the extreme southwest—in Arizona, New Mexico, or Texas. As previously stated such Lows always bring rain as they move northeastward.

Warm Waves. There come in summer periods of almost stagnation in the drift of the Highs and the Lows across the continent. At such times if a High be centered in the South Atlantic Ocean, with its center at Bermuda, and its western limits extending into the South Atlantic coast States, there will result what is popularly known as a warm wave, for the air will slowly and steadily move from the southeast, where the pressure is greater, towards the northwest, where it is less; it will receive constant accretions of heat from the radiating surface of the earth, and finally attain to a temperature that is extremely uncomfortable to all forms of life, that lowers the physical stamina, and that largely increases the death rate. This superheated condition of the lower stratum of air in which we live continues until a Low develops in the southwest and a High in the northwest, which relation, as we already know, soon brings rainfall to the interior of the country.

V-shaped Lows are reasonably sure to cause precipitation, and if the barometer at the center of the Low be five to seven tenths below the outer limits of the depression, heavy precipitation and destructive local storms may be expected.