gives a brief and yet complete résumé of what is perhaps the best
modern practice. In these brief statements the attempt has been made to
put concisely, intelligibly, and _completely_ (if one will but read
each and every sentence as carefully as they were written), the very
latest, most important, and best-established facts, with which every
navigator should be familiar. The paragraph entitled "Intensified
trade-wind belt," for instance, is very important. A close
consideration of the caution expressed in these few lines may prevent a
serious mistake that might be made by a too rigid adherence to the old
rules. The idea is as follows: It has been proved by Meldrum, from his
studies of Mauritius hurricanes, that the SE. trade-winds blow toward a
part of the _track_ of a hurricane, rather than at right angles to the
direction of its center, and it is therefore unsafe to assume that the
center bears at right angles to the wind, or that, because the trade
wind increases in strength without any decided change of direction, the
center is approaching directly toward the vessel. This principle might
naturally be expected to hold for similar storms in other regions, and
Abercromby, in a thorough study of the whole subject, has shown that
such is the case, although he states that "the position of this belt
[of intensified trades] differs in every hurricane region, so that a
special set of rules are necessary for each country." It seems to me, I
must say, that in the absence of such special rules the law may safely
be assumed to be general; its importance to navigators is certainly
very great, and its principal effect must be to urge the greatest
caution in making any attempt to cross the track of a hurricane, from
the dangerous to the navigable semicircle.
{PLATE: WEST INDIAN HURRICANES, AND OTHER NORTH ATLANTIC STORMS.
From the Pilot Chart of the North Atlantic Ocean, August, 1889, with
Additional Paragraphs. [_Edition of July, 1890._]
Explanation.--These diagrams are for practical use in West Indian
hurricanes. The upper one will also answer for ordinary storms along
the transatlantic route. The small arrows fly with the wind, the
direction being stated at the end of each dotted line; the long arrow
on each diagram is the STORM TRACK, that is, the probable path of the
cyclone through the belt of latitude to which the diagram applies.
[Illustration: JUNE and OCTOBER, lat. 23° to 55°. JULY and SEPT., lat.
29° to 55°. AUGUST, lat. 33° to 55°. STORM TRACK, N NE. TO E NE. Motion
of storm center along track, 20 to 30 miles per hour.]
[Illustration: JUNE and OCTOBER, lat. 20° to 23°. JULY and SEPT., lat.
27° to 29°. AUGUST, lat. 30° to 33°. STORM TRACK, N NW. to N NE. Motion
of storm center along track, 5 to 10 miles per hour.]
[Illustration: JUNE and OCTOBER, lat. 10° to 20°. JULY and SEPT., lat.
10° to 27°. AUGUST, lat. 10° to 30°. STORM TRACK, W. by N. to N NW.
Motion of storm center along track, about 17 miles per hour.]
Use of the Diagrams.--When a falling barometer, freshening rain
squalls, &c., indicate a hurricane, select the proper diagram
(according to the MONTH and LATITUDE), plot your position upon it by
means of the direction of the wind, and thus ascertain the approximate
bearing of the storm center. The probable storm track is indicated by
the long arrow. If the wind shift, plot your position by means of the
new wind-direction (nearer the center if the wind has freshened and the
barometer has fallen). In this way you can readily observe every change
of position relative to the storm center, and decide what action to
take, according to the character of your vessel, the lay of the land,
&c. These storms vary greatly in size, but are smallest and most
violent in the tropics, where the cloud ring averages about 500 miles
in diameter and the region of stormy winds 300 miles, or even less. You
can therefore only roughly estimate the DISTANCE of the center,
although its BEARING can be obtained from the diagrams with a high
degree of probability. There is also considerable variation in the
direction of motion and the velocity of the storm along its track, but
the general tendency is as stated herewith.
Cyclonic Circulation.--One of the most important indications that an
approaching storm is of hurricane violence is the marked cyclonic
circulation of the wind, lower and upper clouds, etc. This may be
easily appreciated by remembering that a cyclone of any great intensity
is an ascending spiral whirl, with a rotary motion (in the Northern
Hemisphere) against the hands of a watch, as shown on the diagrams. The
surface wind, therefore, blows spirally inward (_not_ circularly,
except very near the center); the next upper current (carrying the low
scud and rain clouds), in almost an exact circle about the center; the
next higher current (the high cumulus), in an outward spiral--and so
on, up to the highest cirrus clouds, which radiate directly outward.
The angle of divergence between the successive currents is almost
exactly two points of the compass. Ordinarily, with a surface wind from
N., for instance, the low clouds come from N., also; on the edge of a
hurricane, however, they come from N NE., _invariably_. In rear of a
hurricane, the wind blows more nearly inward; with a SE. wind, for
instance, the center will bear about W., the low clouds coming from S
SE. (two points to the right of the wind), etc. Great activity of
movement of the upper clouds, while the storm is still distant,
indicates that the hurricane is of great violence. If the cirrus plumes
that radiate from the distant storm are faint and opalescent in tint,
fading gradually behind a slowly thickening haze or veil, the
approaching storm is an old one of large area; if of snowy whiteness,
projected against a clear blue sky, it is a young cyclone of small area
but great intensity.
Intensified Trade-wind Belt.--Another very important fact (established
by Meldrum, at Mauritius) may be stated thus: When a hurricane is
moving along the equatorial limits of a trade-wind region, there is a
belt of intensified trades to windward of its track: not until the
barometer has fallen about six-tenths of an inch it is safe to assume
that, because the trade-wind increases in force and remains steady in
direction, you are on the track of the storm. By attempting too early
to cross its track, running free as soon as the wind begins to freshen,
you are liable to plunge directly into the vortex of the hurricane.
General Information.--Hurricanes are especially liable to be
encountered from July to October, inclusive, in the tropics (north of
the 10th parallel), the Gulf of Mexico, and Gulf Stream region.
Earliest indications: Barometer above the normal, with cool, very
clear, pleasant weather; a long, low, ocean swell from the direction of
the distant storm; light, feathery cirrus clouds, radiating from a
point on the horizon where a whitish arc indicates the bearing of the
center. Unmistakable signs: Falling barometer; halos about the sun and
moon; increasing ocean swell; hot, moist weather, with light variable
winds; deep red and violet tints at dawn and sunset; a heavy,
mountainous cloud bank on the distant horizon; barometer falling more
rapidly, with passing rain squalls.
Brief Rules for Action.--If the squalls freshen without any shift of
wind, you are on the storm track: run off with the wind on the
starboard quarter and keep your compass course (see caution in
paragraph entitled "Intensified Trade-wind Belt"). If the wind shift to
the right, you are to the right of the storm track: put the ship on the
starboard tack and make as much headway as possible, until obliged to
lie-to. If the wind shift to the left, you are to the left of the storm
track: bring the wind on the starboard quarter and keep your compass
course; if obliged to lie-to, do so on the port tack. In scudding,
always keep the wind well on the starboard quarter, in order to run out
of the storm. Always lie-to on the coming-up tack. Use oil to prevent
heavy seas from breaking on board.}
The next plate,