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In 1884 I suggested the division of typhoons into four classes (Comp.
Observations ar Researches made at the Hongkong Observatory in 1884," app. M) but the final arrangement of s classes could not then be effected:
In B
§ 5.-WINTER TYPHOONS IN THE SOUTHERN PART OF THE CHINA SEA. In the typhoons of the summer months, the SW monsoon period,-which move towards WNW Jaz originate in the China Sea (most frequently near 18 to 20 N and 113° to 116° E) noe area over which the winds become strong with a decided fall in the barometer in front of the or NW in the N part of the China Sea and enter the coast in the neighbourhood of the Gulf of Tongking, of 15° N and enter, or at least approach the mainland to the W of Hongkong. 10 po all the typhoons registered belong to this class. They prevail from the middle of fogking and the continent beyond it.
erre is generally small.
This is accounted for by the low pressure prevailing over the Gulf of till the end of September.
For the same reason the winds in rear are not only stronger originate in the Pacific and enter the China Sea north of 15 N and enter, or at lequently become diffused over a large area.
bat also long continued, the more particularly as it seems that depressions on entering the coast approach the mainland to the W of Hongkong, 12 p.c. of the typhoons belong to
In the autumn months (September and October)---the NE onsoon period, these conditions are reversed and we find that in front pressure begins to give way class. They prevail from the beginuing of July till the middle of October. originate in the Pacific and enter the China Sea north of 15" X, move SW and disapp for the depression is comparatively small. Moreover, at this period the depression fills up rapidly on and strong winds usually blow at great distances, while in rear the area over which winds are governed at sea. Only one or two cases of this kind have ever been registered (late in the year) entering the mainland, which is then dry. In consequence a vessel in front of a typhoon, moving as originate in the China Sea and move N, but describle vastly different paths, movingated, will usually get much shorter notice of the advance of a typhoon from the barometer in summer various directions between W, round by N, to ENE. Sometimes they recurve an in autumn, and while in summer the bad weather lasts a long time in rear, in autumn it improves entering the mainland They occur from June till the end of September, but they a rapidly when the centre is past and a strong NE monsoon sets in. For instance, N gales frequently most common at the beginning of the typhoon season (4 p.c.). originate in the China Sea, where they recurve, and sometimes move into the Pacs off on the E side of the China Sea.
blow late in the season off the Aunam and Cochin China consts with a typhoon centre a long distance passing near South Formosa. They occur from May till September incl, (2 p.c.). Typhoons of classes la and le (26 p.c. of all typhoons) are frequently felt in Hongkong.
CLASS II.
16
Je
Id
Ila
Itb
He
Id
SIT ())"
Typhoons of classes IVa, IVb or 15 occur especially late in the year in an unusually low latitude over the China Sea, during the height of the NE monsoon which blows much stronger in these seas than the SW monsoon. Taking as an example of such, the typhoons of the 15th November, 1891, Eof the 20th November, 1891, and of the 13th November, 1895, it is seen that there is very little W centre, where SW gales might be expected their place is taken by dead calms or light variable winds. S wind except within perhaps at most 50 miles of the centre. And to the S or SSW of the No stronger argument could be adduced to show that the winds round a typhoon-centre are composed of the cyclonic winds on one hand and the prevailing wind on the other. In these cases where the cyclonic SW gales are combined with the NE monsoon gales, calms are the result. Unfortunately, I have not succeeded in drawing the isobars, as the anëroid observations on board ship are too rough to from the wind-directions laid down on the maps. be of much assistance for this purpose, and the currents are strong, but the isobars might be inferred
originate in the Pacific, enter the China Sea north of 15° N, and enter China to the Hongkong. There they pass (Ha) N, or (Ha.) W. They occur in July, Auga and September (2 p.c ). originate in the Pacific and move into the Formosa Channel. They occur from Imet September incl., and are most common in August and September (7 p.c.). originate in the Pacific, pass N of rorniosa, and enter China. They occur from June September, with a distinct maximum in July (3 p.c.),
originate in a high latitude in July and August and move W-ward into China (4 p.) With the exception of Ila, which sometimes cause fierce SW gales in Hongkong, typhoouse Class II are not dangerous to this Colony.
CLASS III.
These typhoons originate and rage mainly in the Pacific.
Illa
IIId
Ille
When all the wind forces round the centre of a typhoon are resolved into N and E components, positive or negative as the case may be, and the resultant direction and velocity are computed and compared with the direction of motion and velocity of the centre, it is found that the latter moves from a greater azimuth (counting from N) than the wind. This might be expected as it then agrees with
different from the resultant wind. As the NE monsoon is shallow, this probably agrees with the direction of the wind at an altitude of about half a mile, but the speed is only a fraction of the resultant wind velocity.
enter the coast of Luzon but recurve (usually before the centre enters the China Say the wind at a greater altitude. These November typhoons move from a direction from 2 to 7 points They prevail in October and November (11⁄2 p.c.).
enter the coast of Formosa but recurve, usually in October (1 p.c.). move N and enter Korea in July, August and September (4 p.c.).
recurve in the Pacific and enter Japan between June and October incl. They are a frequent in August and September (15 p.c).
remain in the Pacific. They occur from May till December incl. Their average latitu decreases on the whole with the altitude of the midday-sun, 10 p.c. of all the typhos registered belong to this class, but there must be many that are not met by ships ase therefore not registered. Their prevalence may be estimated at 124 p.c.).
CLASS IV.
IVa originate in the China Sea south of 15° N and move towards Hainan and Annam. Tie occur from May till December incl., but are rarely encountered in August (8) pe.). l November they often originate in about 11° N and 116° E.
Va B originate in the Pacific and enter the China Sea south of 15o X. They are less conna than those originating in the China Sea, as the long passage across the southern Puli- pines tends to break them up. They occur at the begining and end of the typho season (3 p.c.).
IV6
IVe
IVd
enter the China Sea after crossing the Philippines in a low latitude, and then move Sh and disappear at sea. They occur from the beginning of September till the beginnings December, but are most common in November (44 p.c).
recurve in the China Sea and re-enter the Pacific. They occur at the beginning and of the typhoon season but mostly in May (4 p.c. ),
occur in the Gulf of Siam in April and December (1 p.c.).
The accompanying plate illustrates the average paths of these different kinds of typhoons. T average rate of progress in 24 hours is also marked, but it must be remembered that individual typh move in very irregular orbits, whose vagaries have disappeared from the average paths. Also the travel at very different rates. It is presumably as useful to the travelling public, and the freight carry public to know where and when typhoons prevail, as to the weather-forecaster, who in default of pres observations reaching him by wire, must forecast according to such paths as these.
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1891 Newl5.
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