906 SUPPLEMENT TO THE HONGKONG GOVo GAZETTE OF 2nd OCT., 1886.
difficult to trace the existence of a high pressure area (anti-cyclone) behind the cyclone, simply be the barometer is in any case rising there. But apart from the question of the high pressure may be supposed to follow the cyclone, there does not generally exist a fine weather area behind the S and particularly SW winds blow there very fresh, accompanied by overcast, damp and frequ wet weather. Thunderstorms. likewise follow after a typhoon especially along the coast of sou China. This is easily explained in close analogy with land and sea breezes as for instance wi typhoon has raged in the Formosa Channel and is followed there by overcast, wet and in conseq cool weather, while the fine and hot weather area continues to prevail in Tonquin, Hainan and part of the southern coast of China: the hot air will naturally expand and overflow the coole which will be drawn westward at the surface of the earth, thus generating a vortex motion ro horizontal axis, the recognized adjunct of a thunderstorm. The Easterly squalls occasionally here when a typhoon is passing northwards through the Formosa Channel are thus explained.
From observations made here it appears that within 150 miles of the centre of a typhoon th is densely overcast with nim. clouds accompanied by heavy rain and within 300 miles on an av 90 per cent. of the sky is covered with cum., R-cum or nimbus clouds, above which the different clouds are visible. Within 60 miles of the centre the rain generally pours down in torrents.
Nortl of the centre between 300 and 600 miles away the percentage is 50, the lower clouds being generally above which c-cum. predominate, and between 600 and 900 miles away it is 40, the lower clouds generally cum., above which c-cum. are usually seen. Southwest of the centre between 300 and miles away the average percentage is 60, the lower clouds being cum. or nim. and the upper gen c-cum. or c-str., and between 600 and 900 miles away it is 50, the lower clouds being generally cum-str. or nimbus (the latter predominate straight S of the centre) and the upper, c., c-cum. or c-s Cirrus clouds are found within 1200 miles on all sides of the centre of a typhoon. Thunde lightning are observed in the region covered by eum-str., but not elsewhere. In the small typl that pass South of Luzon lightning is seen nearer the centre.
The average temperature in Hongkong when a typhoon is more than 300 miles away is abou and it rises frequently much higher. Within 300 miles of the centre the temperature falls qu owing to the great amount of heavy clouds. The difference between the temperature at the Peal at the Observatory does not appear to be affected by the approach of a typhoon, but further observ is required to elucidate this point.-The dimensions here given must as far as the inner area is conc be much reduced in case of a typhoon in a low latitude, while above 30° latitude the circumst appear to be more irregular than farther south. Very near the centre the temperature at sea is gen about 76° and on shore about 78°.
Rain fallen during a typhoon is not accurately measured in a well exposed gauge as the str of the wind to a great extent prevents its falling into the gauge. More rain falls in sheltered spc where the force of the wind is broken by an obstacle.
The diameter of the bull's eye of a typhoon between 10° and 15° latitude is about 4 miles 25° latitude it appears to be occasionally as much as 30 miles in diameter, but bull's eyes of diameter have been found in case of typhoons crossing Japan. This area is characterised by very winds or perhaps occasionally by perfect calms. Generally the sea is mountainous but occasiona calms down to some extent together with the wind. A downrush of air in the bull's eye of a typ is out of the question as the sky there is covered with light clouds, but on the other hand it is ev from the clearing of the sky that the uprush of air has ceased or almost ceased.
That the centre of the bull's eye does not coincide with the centre of all the directions of the when projected on a diagram may to some extent be caused by the ellipticity and excentricity ‹ isobars.
The gradients corresponding to a certain force of wind is somewhat uncertain partic when the force of the wind exceeds a whole gale, but it does not seem to be perceptibly affected b latitude. It should be remembered that the average temperature in the typhoon season does not ch much with the latitude in the area here under discussion: On an average a gradient of 0.02 inch 15 miles corresponds to a force of wind 6 on Beauforts scale, 0.03 to 7, 0.04 to 8, 0.05 to 9, 0. 10, 0.10 to 11 and where the gradient is above 0.10 it generally blows with full typhoon force low latitudes the gradient occasionally exceeds one inch in 15 miles.
The wind blows generally with the force of a strong breeze within 300 miles of the centre bet 20° and 25° latitude. but in 12° latitude it appears that it does not attain this force till within 100 miles of the centre. The force of the wind is however different in different azimuths. Near it is frequently very irregularly distributed. The wind blows in gusts in a typhoon. More da is however done to ships by the high cross seas always experienced near the centre,
The swelli within from 300 to 500 miles of the centre but this depends of course upon the situation of the la
The angle between the direction of the wind and the direction of the gradient is on an av 43° in front of the centre and 53° behind the centre between 10° and 25° latitude,-65° in fron 85° behind between 30° and 35° latitude,—and 49° in front and 62° behind between 10° an latitude. The angle appears to be smaller near the shore than on the open sea for offshore winds. far out at sea, the difference between the angle in front and behind the centre appears to be small