The Hurricane Guide | Page 2

hurricane with the wind S.E.,--the letters within the two larger circles indicating the direction of the wind in the storm according to the rotation as shown by the circle of arrow-heads, and which it is to be particularly noted is in the northern hemisphere contrary to the direction in which the hands of a watch move: in the southern hemisphere the rotation is reversed--the only ph?nomena presented by the storm are as follows:--The wind continues to blow from the S.E., increasing considerably in force with the barometer falling to a very great extent until the centre of the storm reaches the ship, when the fury of the winds is hushed, and a lull or calm takes place, generally for about half an hour, after which the wind springs up mostly with increased violence, but from the opposite quarter N.W., the barometer begins to rise, and as the storm passes off, the force of the wind abates.
The point to which we wish particularly to direct attention in connexion with this exposition of the ph?nomena attending the transmission of a storm is this:--If the observer so place himself at the commencement that the wind passes from his left hand towards his right, his face will be directed towards the centre of the storm; and the wind undergoing no change in direction, but only in force, will acquaint him with this important fact that the centre is not only gradually but surely approaching him: in other words, in the case before us, when he finds the wind from the S.E., and he places himself with his face to the S.W. he is looking towards the centre, and the wind rushes past him from his left to his right hand. Now the connexion of the barometer with this phase of the storm is falling with the wind from left to right, the observer facing the centre while the first half is transiting.[1] During the latter half these conditions are reversed, the observer still keeping his position, his face directed to the S.W., the barometer rises with a N.W. wind, which rushes past him from his right to his left hand with a decreasing force. We have therefore a rising barometer with the wind from right to left during the latter half of the storm, the observer having his back to the centre.
The above general enunciations of the barometric and anemonal ph?nomena of a rotating storm hold good with regard to the northern hemisphere, whatever may be the direction in which the hurricanes advance. This may be placed in a clearer light, as well as the remaining classes of ph?nomena shown, by consulting the following tables, constructed for the basin of the Northern Atlantic, and comparing them with fig. 1. In this basin, with lower latitudes than 25°, the usual paths of the hurricanes are towards the north-west, in higher latitudes than 30° towards the north-east. The tables exhibit the veering of the wind with the movements of the barometer, according as the ship is situated in the right or left hand semicircle of the hurricane. It must here be understood that the right and left hand semicircles are determined by the observer so placing himself that his face is directed towards the quarter to which the hurricane is advancing.
LOWER LATITUDES.
NORTHERN HEMISPHERE.
Axis line, wind N.E., barometer falling, first half of storm. Axis line, wind S.W., barometer rising, last half of storm.
RIGHT-HAND SEMICIRCLE.
Wind E.N.E., E., E.S.E., S.E., barometer falling, storm increasing. Wind S.S.W., S., S.S.E., S.E., barometer rising, storm passing off.
LEFT-HAND SEMICIRCLE.
Wind N.N.E., N., N.N.W., N.W., barometer falling, storm increasing. Wind W.S.W., W., W.N.W., N.W., barometer rising, storm passing off.
HIGHER LATITUDES.
NORTHERN HEMISPHERE.[2]
Axis line, wind S.E., barometer falling, first half of storm. Axis line, wind N.W., barometer rising, last half of storm.
RIGHT-HAND SEMICIRCLE.
Wind S.S.E., S., S.S.W., S.W., barometer falling, storm increasing. Wind W.N.W., W., W.S.W., S.W., barometer rising, storm passing off.
LEFT-HAND SEMICIRCLE.
Wind E.S.E., E., E.N.E., N.E., barometer falling, storm increasing. Wind N.N.W., N., N.N.E., N.E., barometer rising, storm passing off.
N.B. The directions of the hurricane winds are so arranged as to show the points of commencement and termination. Thus in the lower latitudes a storm commencing at E.N.E. passes off at S.S.W. after the wind has veered E., E.S.E., S.E., S.S.E., and S., being in the order of the letters in the upper line and contrary to their order in the lower. One commencing at E.S.E. passes off at S.S.E. right-hand semicircle. In the higher latitudes a ship taking the storm at E.N.E. will be in the left-hand semicircle, and the hurricane will pass off at N.N.E. These changes are rendered very apparent by moving the hurricane circle in the direction in which the storm is expected to proceed.
Fig. 2 represents the whirl and hurricane winds in the south.
[Illustration: Fig. 2]
CHAPTER II.
PH?NOMENA OF ATMOSPHERIC WAVES.
Professor Dove of