Dust devil (also known as dust whirl or sand whirl) resembles tornado at first glance. While both weather phenomena are in the form of whirling column, the wind strength of dust devil is weaker and normally causes less serious damage. The formation of a tornado is generally accompanied by mature cumulonimbus or even thunderstorms, whereas dust devils occur under generally fine weather condition.

On 14 July 2021, dust devil was observed over the construction site of the Hong Kong International Airport (HKIA) at about 2 pm. The related video is as follows:

Formation of dust devil is usually associated with heated and rapidly rising air close to the ground surface. Some favourable meteorological and geographical conditions for the formation of dust devil are listed below:
1. Clear sky or less clouds: Abundant sunshine heats up the air near the ground which is favourable to generation of rapidly rising air.
2. Weak background wind: The whirling structure of rising air will be destroyed if the background wind speed is too high, making it difficult to maintain the dust devil.
3. Flat terrain: Flat ground surface can absorb heat energy from the Sun more effectively. If the surface is sandy or dusty, the sand and dust drawn into the whirling air render the dust devil more visible.

On the day of dust devil observation, a ridge of high pressure affected the south China coastal areas. The weather was mainly fine in Hong Kong. At around 2 pm, the cloud amount observed at the HKIA was 5 oktas (8 oktas for overcast sky). Winds were light to moderate with air temperatures rising to 34 degrees Celsius. The meteorological conditions basically fulfilled the conditions for the formation of dust devil.

It is worth to mention that dust devil can rotate clockwise or anticlockwise. This is because in such a small scale, the effect of Coriolis force cannot come into play.