INDICATIONS OF APPROACHING OR EXISTING HURRICANES, MANIFESTED BY THE
OCEAN, OF ESPECIAL UTILITY TO VESSELS AT ANCHOR IN ROADSTEADS.
1. A swell, produced by the storm-wave, rolling in upon the shore,
at first of a gentle character. The direction of this swell will
pretty surely indicate the bearing of the storm, and its changes
will point out in some localities the course the hurricane may be
pursuing.
2. A swell rolling in, without changing its direction, may be
regarded as indicative of a hurricane approaching the shore.
The same phenomenon met with at sea (the ship’s course being
taken into account) will indicate the bearing down of the
cyclone on the vessel.
3. A dirty green appearance of the ocean; on some occasions its
assuming a muddy or brown color, on others its being remarkably
clear, its temperature increasing, and its swellings stronger
than at other times,—are all indications of the proximity of
a cyclone.
The area over which these rotary storms have been known to expand,
varies from 30 to 40 to 1,000 miles; but while the diameter, so long
as the storm is within the tropics, expands but very gradually, it
suddenly increases in a remarkable manner after recurving. The rate at
which they travel on their onward course also varies greatly, not only
in different parts of the globe, but even in the same locality, and
at the same season. Generally, however, the rapidity with which the
vortex of the hurricane progresses is greater as the storm recurves
on reaching the outer edge of the trade winds. Thus, the hurricane of
August, 1853, traversed 6,276 English miles in about twelve days, with
a mean progressive velocity of twenty-six miles per hour; but after it
arrived at the Banks of Newfoundland this velocity was increased to
about fifty miles per hour.
Within the area of the cyclone the moving body of air frequently
attains a rotatory velocity of from seventy to one hundred miles
an hour.
TABLE SHOWING THE DIFFERENT MONTHS OF THE YEAR IN WHICH HURRICANES AND
CYCLONES HAVE BEEN RECORDED IN VARIOUS REGIONS.
══════════════════════╤═══╤═══╤═══╤═══╤═══╤═══╤═══╤═══╤═══╤═══╤═══╤═══
LOCALITY. │Jan│Feb│Mar│Apr│May│Jun│Jul│Aug│Sep│Oct│Nov│Dec
──────────────────────┼───┼───┼───┼───┼───┼───┼───┼───┼───┼───┼───┼───
│ │ │ │ │ │ │ │ │ │ │ │
No. Atlantic and W.I. │ 5 │ 7 │ 11│ 6 │ 5 │ 10│ 42│ 96│ 80│ 69│ 17│ 7
│ │ │ │ │ │ │ │ │ │ │ │
South’n Indian Ocean │ │ │ │ │ │ │ │ │ │ │ │
& Mauritius. │ 9 │ 15│ 15│ 8 │ 4 │ │ │ │ 1 │ 1 │ 4 │ 6
│ │ │ │ │ │ │ │ │ │ │ │
North’n Indian Ocean; │ │ │ │ │ │ │ │ │ │ │ │
Bay of Bengal— │ │ │ │ │ │ │ │ │ │ │ │
N.E. Monsoon. │ 1 │ │ 3 │ │ │ │ │ │ │ 12│ 7 │ 6
S.W. Monsoon. │ │ │ │ 6 │ 16│ 4 │ 1 │ 2 │ 1 │ │ │
│ │ │ │ │ │ │ │ │ │ │ │
Arabian Sea & Bomb’y— │ │ │ │ │ │ │ │ │ │ │ │
N.E. Monsoon. │ 1 │ 1 │ 1 │ │ │ │ │ │ 8 │ 12│ 9 │ 5
S.W. Monsoon. │ │ │ │ 5 │ 9 │ 2 │ 4 │ 5 │ │ │ │
│ │ │ │ │ │ │ │ │ │ │ │
China Sea and North │ │ │ │ │ │ │ │ │ │ │ │
Pacific— │ │ │ │ │ │ │ │ │ │ │ │
(western part). │ │ 1 │ │ │ 2 │ 2 │ 12│ 5 │ 18│ 14│ 12│ 1
│ │ │ │ │ │ │ │ │ │ │ │
Java Sea and Northwest│ │ │ │ │ │ │ │ │ │ │ │
Coast of Australia. │ 3 │ 5 │ 1 │ 1 │ 2 │ │ │ │ │ │ │ 2
──────────────────────┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───
From this table it appears that the hurricane seasons in the several
localities are as follows:
1. In the North Atlantic, from June to November, the greater number
occurring in July, August, September, and October.
2. In the Bay of Bengal they are most prevalent in October, November
and December, when the N. E. Monsoon is strongest; they occur also
during the S. W. Monsoon, especially in April, May or June.
3. In the Arabian Sea they have been experienced during both
Monsoons.
4. In the China Sea they are prevalent on the coast between June and
October; but in the central part of that sea during September,
October and November.
5. In the Southern Indian Ocean they may be expected between November
and April, but they are most prevalent during January, February
and March.
6. In the Java Sea, and on the N. W. Coast of Australia they have
been recorded during December, January and February.