With Super Typhoons Near Hong Kong, Small Variations in Tracks Mean Huge Differences in Impacts

Occasionally, typhoons have caused immense damage and loss of life in Hong Kong; the worst effects arise from storm surges, which are somewhat akin to tsunamis accompanied by mighty waves; see Hong Kong Typhoons including Calamitous Storm Surges.

But also, even powerful typhoons can approach Hong Kong, and pass by without causing much damage. So what’s going on?

It turns out, there’s something akin to a “lottery”, with various factors involved in typhoon damage – not just the strength of winds around the eye, but also the size of storms, speeds they travel [the more time over/near Hong Kong, the more chance of damage] and especially the tracks.

Here, say, are the tracks of five typhoons that resulted in storm surges in Hong Kong; all approach from the east-southeast, mostly passing through the Luzon Strait with no significant interactions with land to weaken them (Mangkhut differed, with its eye just passing over the north tip of Luzon, which disrupted its structure and intensity):

Notice how Wanda, and the unnamed typhoons in 1906 and 1937, passed very close to or over Hong Kong. They also caused the more extreme storm surges; with the two unnamed storms also causing over 10,000 deaths.

The 1936 storm had a similar path, yet was perhaps 20km south of the typhoon a year later – a relatively small difference in distance and track, yet the storm surge was considerably less destructive.

Even mighty Mangkhut, the main typhoon to hit Hong Kong so far this century, brought a surge with memorable images of waves breaking at Heng Fa Tsuen, eastern Hong Kong Island, yet its large eye remained to the south.

Yet even as typhoons pass perhaps 100km or more to the south of Hong Kong they remain over the sea, and hence may lose relatively little power, which means they can still push surges and waves to the coast, along with strong and hurricane force winds.

Contrast Usagi, in 2013. As this typhoon approached, there were concerns in the Hong Kong Observatory that it might cause damage akin to historic typhoons. Yet as it appeared perhaps set for a direct hit, it made a slight turn towards the north – making landfall to the east of Hong Kong, and then quickly losing intensity so it was of relatively little consequence in Hong Kong: