Typhoon Elsie, 1975

       Typhoon Elsie was one of the most intense typhoons that have affected Hong Kong in October. It was also the first occasion that required the hoisting of the Hurricane Signal, No. 10, since Typhoon Rose in August 1971. Although there were storm to hurricane force winds during the passage of Elsie, relatively minor damage was experienced possibly as a result of the timely warnings issued by the Royal Observatory.

       Elsie originated as an area of low pressure about 400 miles west-southwest of Guam on October 9. It moved west-northwest at about 10 knots towards the Bashi Channel and intensified into a severe tropical storm the next day. Early on the morning of October 10, a reconnaissance aircraft reported maximum surface winds of 70 knots and a minimum sea-level pressure of 989 millibars near its centre. Satellite pictures received at the Royal Observatory also indicated that Elsie had become well organized with a circular eye and intense spiral rainbands (Figure 2).

        Elsie further intensified into a typhoon on October 11. At 5.52 a.m. on the same day, a reconnaissance aircraft reported that the minimum sea-level pressure near the centre of Elsie had dropped to 974 millibars. Maximum winds estimated from satellite pictures received at the Royal Observatory later in the morning were about 90 knots (Figure 3). The central pressure fell further to 900 millibars and maximum surface winds of 130 knots were reported by a reconnaissance aircraft at 12.40 p.m. on October 12. Meanwhile, the storm slowed down slightly but still continued to move west-northwestwards towards the Bashi Channel. Satellite pictures received at the Royal Observatory earlier in the morning indicated that the cloud mass of Elsie covered an area about 300 miles in diameter and maximum winds were estimated to be about 115 knots (Figure 4).

        In Hong Kong, the Stand By Signal, No. 1, was hoisted at 10.45 p.m. on October 12 when Typhoon Elsie was about 400 miles east-southeast of Hong Kong and was moving west-northwest at about eight knots towards the northeastern part of the South China Sea.

       Having crossed the Bashi Channel, Elsie turned onto a more westerly track. By late afternoon on October 13, the eye of the typhoon began to appear on the Royal Observatory's weather radar and could be tracked easily as the typhoon was very well organized with good spiral rainbands ahead of the centre and a tight circular eye of about 20 miles in diameter (Figure 5). The eye was located accurately as it was also tracked simultaneously by the Kaohsiung radar.

        The Stand By Signal was replaced by the Strong Wind Signal, No. 3, at 8.00 p.m. on October 13 when Elsie was about 190 miles east-southeast of Hong Kong. Statements were issued by the Royal Observatory to warn the public to take precautionary measures as Elsie was expected to remain intense and might pass very close to Hong Kong, although local winds were then generally only light to moderate westerly.

       On October 14, the No. 8 Northwest Gale or Storm Signal was raised at 4.30 a.m. when the centre of Elsie was about 100 miles east-southeast of Hong Kong. At this time, winds over Hong Kong were only moderate to fresh in strength from the northwest. Winds increased rapidly as Elsie moved closer during the day and gales were first reported at 9 a.m. on October 14 when Elsie was about 70 miles east-southeast of Hong Kong.

       Elsie remained very well organized and continued to move westwards (Figure 6). At 11.00 a.m. on October 14, the Increasing Gale or Storm Signal, No. 9, was hoisted to warn a significant increase in wind speed over Hong Kong when Elsie was centred only about 40 miles to the southeast. The eye of the typhoon had become smaller and was then only 10 miles in diameter. During the early afternoon of that day, as there were definite indications that the eye of the typhoon would pass close to the south of Hong Kong lsland and also over the waters of Hong Kong, the Hurricane Signal, No. 10, was hoisted at 2.15 p.m. to warn the public that winds were expected to veer to the east and reach hurricane force offshore and over the southern parts of Hong Kong. Elsie was closest to Hong Kong at 2.30 p.m. when it was centred about 27 miles south of the Royal Observatory and was then moving west at eleven knots. During the afternoon, winds of 70 knots with gust peak speeds of 97 knots at Tate's Cairn, and 76 knots with gust peak speeds of 118 knots at Stanley. The mean sea-level pressure at the Royal Observatory dropped to a minimum of 996.2 millibars shortly after 3 p.m. and rose sharply after the passage of the typhoon. The lowest mean sea-level pressure in Hong Kong was 987.5 millibars, recorded at Waglan lsland around 2.30 p.m. on October 14.

       A radiosonde ascent made at 2.02 p.m. on October 14 showed that Elsie began to weaken while passing to the south of Hong Kong. The relatively high sea-level pressure experienced in Hong Kong was probably a result of the entrainment of cold air from an intense anticyclone over China. Radar pictures taken at the Royal Observatory also showed that the eye of the storm gradually filled with rain (Figure 5d). As Elsie started to move away from Hong Kong later in the afternoon, winds turned easterly and began to moderate. The Hurricane Signal was replaced by the No. 8 Southeast Gale or Storm Signal at 5.05 p.m. when Elsie was 29 miles south-southwest of Hong Kong, and was followed by the Strong Wind Signal at 8.10 p.m. when Elsie was about 40 miles southwest of Hong Kong.

       During the evening of October 14, Elsie resumed a west-northwesterly track and weakened further to a tropical storm. It crossed the south China coast about 60 miles west-southwest of Hong Kong shortly after 10 p.m. on the same day. Local winds continued to subside and all signals were lowered at 2.00 a.m. on October 15 when the storm was about 80 miles west of Hong Kong. Elsie was downgraded to a tropical depression during the following hour and subsequently dissipated overland about 100 miles west of Hong Kong early on the morning of October 15 as cool northeasterly monsoon began to affect the south China coast.

       During the passage of Typhoon Elsie, hurricane force winds were recorded for 2 hours at Tate's Cairn, for 1 hour at Waglan lsland and for 4 hours over the southern parts of the Hong Kong lsland. Sustained gale force winds were experienced practically everywhere in Hong Kong except in some sheltered urban areas. Cheung Chau recorded continuous gales for the longest period of 13 hours. Gales were also recorded for 8 hours at Waglan lsland, 5 hours at the Hong Kong Airport, and 12 hours at Tate's Cairn.

       The weather in Hong Kong was fine, sunny and hot on October 12 and 13 before the approach of Elsie. It became cloudy on the morning of October 14 with scattered showers which became more frequent and squally during the day. Early in the afternoon, heavy rain set in as Elsie moved closer to Hong Kong. The rain was heaviest between noon and 2 p.m. when Elsie was passing to the south of Hong Kong. Later in the afternoon, the rain subsided slightly as Elsie moved away from Hong Kong. The weather remained cloudy to overcast with patches of light rain and occasional squally showers on October 15. Because of the onset of an easterly monsoon surge, there was not much improvement in the weather on the following day.

       Elsie was an intense typhoon as far as wind strength was concerned, but rainfall was not exceptionally heavy (Figure 7). Although intense spiral rainbands were observed ahead of the eye, Elsie had a comparatively small circulation of about 300 miles in diameter. The total rainfall of 150.6 mm agreed well with the amounts predicted by the Royal Observatory.

       The following daily amounts of rainfall were recorded at the Royal Observatory:

       As maximum winds occurred at the time of low tide, no serious flooding was reported although huge waves spilled over many waterfront streets. The maximum wind-generated waves recorded at Waglan Island were about 9.5 metres at noon and around 3 p.m. on October 14. The times and heights of the highest tides and maximum storm surges recorded at various locations in Hong Kong during the passage of Elsie were as follows :

       Five ocean-going vessels drifted from their moorings but no serious damage was reported. One small craft and a fishing junk capsized and another fishing junk ran ashore.

       Forty-six people were injured by flying glass and collapsing scaffolding but fortunately there were no fatalities. 1277 people sought refuge in shelters when their homes were threatened by strong winds. Altogether eighty-five incidents were reported mostly of a minor nature involving trees, scaffolding, fallen traffic signs and lamp posts. However, in some places, the winds were so strong that the Hurricane Signals could not be raised and at Waglan lsland the signal mast was blown down. Traffic of all kinds was disrupted.

Remarks: (i)  Royal Observatory was the title of the Hong Kong Observatory from 1912 to 30 June 1997. (ii) Unit Conversion - 1 knot 1.852 kilometre per hour (km/h) 1 nautical mile 1.852 kilometre (km) 1 millibar = 1 hectopascal (hPa) (iii) Transformation of Tropical Cyclone Warning Signal System in H.K. Years Tropical Cyclone Warning Signal No. 1956 - 1972 1 3 5 6 7 8 9 10 1973 onwards 1 3 8NW 8SW 8NE 8SE 9 10