No room for complacency

Hong Kong survived the direct onslaught of Typhoon Victor on August 2 with comparatively little damage.

However, as someone interested in meteorology, I was intrigued by some reports in the Chinese press which attributed such minimal damage to the improvement in society and the forecast system. While these factors are relevant in minimising injuries and damage to property, most of these reports were based on a fundamental scientific misconception about wind speeds.

Some of the reports alleged that Typhoon Victor was comparable in magnitude with Typhoons Wanda and Ellen which battered the territory in 1962 and 1983 respectively, by saying that all these storms packed winds of up to 100 'knots'. Well, there lies the error and the root of their misconception.

Prior to the end of the 1980s, wind speeds in Hong Kong were expressed in 'knots' (that is, nautical miles per hour). Thus, hurricane force winds were defined as winds which reached, or exceeded, 64 knots. However, since the late '80s, wind speeds have been denoted in 'kilometres per hour' (kph). Nowadays, hurricane force winds are winds which reach, or exceed, 118 kph. As one knot is equivalent to 1.852 kph, when comparing wind speeds quoted in the different eras, a simple mathematical conversion is necessary. According to the Observatory, the peak winds of Victor reached 125 kph in the afternoon of August 2, before it hit Hong Kong.

According to records, the maximum wind speed recorded over Hong Kong during the passage of Wanda was 154 knots (that is, 285 kph), and that for Ellen was 134 knots (248 kph). Therefore, it should be immediately apparent that Victor, even though it passed directly over the territory, was less than half as powerful as her famous predecessors.

Furthermore, it weakened into a severe tropical storm after making landfall and there was no need to hoist the No. 10 signal. (This should be contrasted with the cases of Wanda and Ellen when the No. 10 signal was put up for eight hours on both occasions).