02
It is important that seamen should realise that the position of the centre of the typhoon as signalled is the position according to the data possessed by the Royal Observatory at the time of the issue of the warning. That data may be as much as 12 hours old. Thus, if the time signal indicates that the warning was issued “This morning," it may be that the position corresponds to data concerning yesterday afternoon.
If the signal "Deepening" is made, it indicates that there is reason to believe that the barometric gradient and, consequently, the intensity of the typhoon is increasing.
C.
If the signal Exceptional velocity" is made, it indicates that there is reason to believe that the rate of
progression is 25 per cent, or more greater than the
average rate.
LATITUDE.
Ordinary
03
BEFORE RECURVING.
AFTER RECURVING.
Limits.
Mean.
Exceptional
signalled.
Maximum
recorded.
Velocity as
ܪ1
Limits.
Ordinary
Mean.
Exceptional
Velocity as
signalja.
Maximum
recorded.
5 10 15
5 10 12 Q 11
22
20 5
14
24
5 10 17
13
22
20
* 25
1 1
3
21
30
25
30
13 EF 1༣
JI
18
--
23
35
10
79
36 ZO 25
+2
16
1 Z
36
2 J
26)
1
36
21 : 26
+8
12
36 21 16
12
"
1 37
26
+9
30
50
Seamen should realise that, whatever may be the probability of a certaiu velocity in a given case, there is always the possibility that it may be greatly exceeded, The safest guide is to make allowance for extreme velocity.
If the signal
54
Position uncertain * is made, it indicates that the data possessed is unreliable and that the position signalled is a mere probability.
The several tracks which a typhoon may follow in the several months are very varied, and the velocity of progression is liable to be erratic. It is not safe to count on a typhoon maintaining a velocity indicated by previous positions of its centre. The velocity is liable to increase very suddenly. Seamen are recommended to study from available sources the tracks and average velocities for the month and locality concerned. In the absence of more exact information the following table of velocities in knots for the several latitudes may be useful.
TYPHOON SIGNAL.
Time
Direction
Latitude
Longitude
Radius, etc.
A severe typhoon within 30 miles of lat. 26° N., long. 120° E., travelling N.E. Warning issued this morn- ing.
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