MONTHLY WEATHER REVIEW ALFRED J. HENBY. Editor.
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CLOSED JUNE 3, 1922
ISSUED JUNE 24, 1922 APRIL, 1932. VOL. 50 No. 4.
W. B. No. 772.
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DISCONTINUANCE OF CHART I---HYDROGRAPH OF SEVERAL PRINCIPAL RIVERS.
Beginning with this issue, the above-named chart will be permanently discontinued and the serial numbers of the remaining charts regularly published will each be advanced one number; thus the previous No. I1 will now be No. I, etc.
The infonnat.ion carried by this chart is nblished in tabular form, annually, in the volume gaily River Stages. Considerable inquiry shows that the purpose of t,he chart thus discontinued will be equally well served by the data of Daily River Stages.-EDITOR.
FORMATION AND MOVEMENT OF WEST INDIAN HURRICANES.
By EDWARD H. BOWIE, Meteorologist.
[Weather Bureau, Washington, D. C., May 3,1922.1
SYNOPSIl.
The physical features of the hurricane are fairly well understood. The explanation of the process of formation of the hurricane remains in more or less dispute, there being two hypotheses t,hat att.empt to shsfactorily explain its origin. There are rewons for believing that countercurrents. hwing their origin in differences in tcmperat.ure over large pqraphic areas. initiate the condit.ions that give rise t.0 the swtem of gyrating winds: that the condensstion of water vapor supplies the energy necessary to maiutain them through consideralh periods of time. The movement of the hurricane is qnerally attributed Do
the general drift of the air in the region of the hurricane. The daily synoptic weather charta and the observations of the free-dr directions and speeds of the winds in regions contiguous to hurricanes appear t,o indicate that hurricanes are carried forward on the border of the major wind system (the northeast trade) of the tropics, and that it8 this x-in.d
s tem changes its direction the coiirse followed by the hurricane 18
cranged to correspond thereto.
The hu,rricane.--To the cydone of the West Indies has been given the name hurricane, a vast systeni of g ating
small and more or less circular region of calnis known as the eye of the cyclone. The movement of the winds around this center is counterclockwise, with varying degrees of inclination and at speeds pro ortional to the stee ness of the baric gradient. The p\ysical features
to Bigelow and other writers, the H, prou.ch of a hurri-
tion to make such observations, by. a long swell on the ocean, propa ated to great distances and forewarning
rise in the barometer a t times occurs before the gradual fall sets in, which fall becomes very pronounced on the near approach of the center; fine wisps of cirrus clouds are first seen, which surround the center to H, distance of 300 miles or more; the air is calm and sultry and the usual afternoon thundershowers are suppressed; this is gred- ually supplanted by a gentle breeze, and later the wind increases to a gale, the clouds become matted, the sea rough, rain falls, and the winds become gusty and dan- gerous as the vortex core comes on. Here is the inde- scribable tempest, dealin destruction, im ressing the
aerial currents, surrounding a central small or re 7 atively
of t R e hurricane are fairly well understood. Accordhig
cane is usually indicated, when the o g server is in a posi-
the observer % y two or three days in rare instances. A
imagination with ita wil 5 exhibition of. tg e forces of
.1m1--1
nature: the torrents of rain, the cooler air by relason o the falling rain, all the elements in an uproar, indicate the close approach of the center. In the midst of this turnioil there is a sudden pause, the winds almost cease, the sky clears, the waves, however, rage in turbulence. This is the eye of the storm, the core o the Tortes, and it is perhaps, 20 niiles or less in diameter, or one-thirtieth the diameter of the whole cyclone. The respit,e is brief and is soon followed by tshe abrupt renewal of the violent wind and rain, but now comin from the
severd features following each other in the reverse order. Re ion of.first appeara,nce.-The hurricane belt of the Nort f Atlantic Ocean extends entirely across the ocean in low lat.itucles, but in so far as we are concerned it may be described and defined as that area extending from longibucle 5G' west to 95' west and from latitude .loo to approximately latitude 35', or roughly the Caribbean Sea, the Gulf of Mcxico, and the waters adjacent to the West Indian Islands. There are, of course, instances where hurricanes have entered this area from the east- ward, but during a period of 35 ears 90 per cent of the hurricanes of these waters accor2ng to Fassig, have had their origin within and not without this area. There is a well-marked belt of maximum Irequency through the northern half of the Caribbean Sea, extending almost due west from the Windward Islands to Yucatan. During the greater part of the year this region and the water areas to the north and east are under the influence of the more or less ermanent area of high barometer of higher
but occasionally the northeast trade wit,hclraws from this region and there is left a region of very slight baric gradient, iriore or less homogeneous temperature dis- tribution in the horizontal, and feeble winds. It is during such times that hurricanes are likely to be found in these waters. Some years ass without hurricane
The formation o hurricanes.-We do not know all e
tioned explanation of the origin of a hurricane. h a t
$eat
opposite direction, and the cyclone passes o E with the
latitudes, an s the northeast trade flows entirely over it,
ti! formations; other years are nota t le for their frequenc .
fects which woul d permit an authoritative and un ues-
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