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Jess Ma

People could smell it in the air and even see it – the arrival of springtime in Hong Kong is heralded by a surge in humidity and residents woke up on Tuesday to slippery floors and walls dotted with water droplets.
As the city hit 100 per cent relative humidity and people complained about the moisture-laden atmosphere, the Post explains why Hong Kong turns damp every year and what to look out for.
1. What is relative humidity and what does 100 per cent mean?
Relative humidity is a measure of the amount of water vapour in the air compared with the maximum amount of moisture that can exist in it at a set temperature.
When the relative humidity reaches 100 per cent, this means the air is saturated with moisture.
If the air cools under these conditions, fog and clouds form as water vapour condenses.

2. Why does Hong Kong get so humid during spring?
Hong Kong is sometimes affected by warm and humid maritime airstreams from the south in the springtime. As the warm air mass gets cooled along the coast of Guangdong province, fog can be formed around the city.
Condensation can form on walls, floors and glass panels as the warm air meets the lower surface temperature of buildings in the city.
3. How long will the humid spell last?
The Hong Kong Observatory said a surge of the northeastern monsoon was expected to reach the city on Wednesday, which would bring cooler air from the Asian continent and lower humidity levels.
Hongkongers wake up to damp buildings, slippery floors as humidity hits 100%
The wind direction is expected to shift from Tuesday’s south and south-easterly winds to moderate northerly winds on Wednesday. That means colder air from the north will blow over the city.
Forecasters said the city was expected to remain humid on Wednesday morning, but that the start of the northeastern monsoon would see temperatures drop and the wind direction change.

4. What is the northeastern monsoon and how will it affect us?
The northeastern monsoon is cold air that flows from high pressure regions on the Asian continent to lower pressure areas.
The band of high pressure causes air to descend to ground level, reducing the formation of clouds and bringing clear weather.
Low pressure regions cause air to rise, which helps in the formation of clouds and fog as the air cools as it ascends.
Hot, humid weather forecast for Hong Kong, before mercury hits 14 degrees Celsius
5. Will humidity cause health problems?
Edmund Lam Wing-wo, a family doctor, said the human body needed time to adjust to rapid changes in temperature and humidity and that people could feel unwell and even require medical attention.
“When our bodies face a lot of environmental variations, it is less healthy,” Lam said.
He said humid weather could worsen allergies and make transmissible diseases even more infectious as droplets could form easily and be sustained in moist air.
He added elderly people and children might need more time to adjust to weather changes and become more susceptible to infectious diseases such as Covid-19, irrespective of their previous infection record.
Lam advised using a dehumidifier to keep a room’s relative humidity at between 40 and 60 per cent.

6. What can you do if you don’t have a dehumidifier?
Mak Yuk-chun, chairwoman of the Hong Kong Domestic Workers General Union, advised the public to keep their windows closed or open a little and turn on fans at low speed if they did not have a dehumidifier.
“It’s the wind. It will deposit moisture everywhere in the house and cause objects to go mouldy,” Mak said.
She added that people should watch out for food going mouldy in the kitchen and wipe down bathrooms after showers and beware of convection drafts, which could bring moisture into flats.


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Slippery floors, water droplets on walls give Hong Kong residents plenty to sweat about. How do you beat soaring humidity levels? Here’s a guide

Moisture build-up on the ceiling in the entrance to a block of flats in Tsing Yi. Photo: Handout

High humidity brings foggy weather to The Peak. Photo: Xiaomei Chen

Ceilings, walls and floors stream with water at a block of flats as humidity hits 100 per cent. Photo: Facebook/Tsing Yi resident group

A cable car at Ngong Ping, Lantau Island, heads into the mist caused by humid weather. Photo: Elson LI

Too humid to handle: Hongkongers wake up to damp buildings, slippery floors amid muggy weather

A foggy day on The Peak. Humidity reached 100 per cent on Tuesday. Photo: Xiaomei Chen

People pass by the Tsim Sha Tsui waterfront. Internet users shared pictures showing water droplets forming on the surfaces of ceilings and walls. Photo: Jelly Tse

Hong Kong Observatory forecasts warmer weather, high humidity next week before temperature expected to hit 14 degrees Celsius

People pose for photos in Tsim Sha Tsui as the weather gradually becomes warmer. Photo: Jelly Tse

A woman wears a “facekini” as temperatures in the city gradually become warmer. Photo: Jelly Tse

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Advice on how to deal with damp as humidity levels hit 100 per cent and moisture accumulates
Forecasters say relief is in sight and humidity expected to start to drop after Wednesday morning


Advice on how to deal with the climate as humidity levels hit 100 per cent and moisture accumulates.


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Explainer | Slippery floors, water droplets on walls give Hong Kong residents plenty to sweat about. How do you beat soaring humidity levels? Here’s a guide

Advice on how to deal with damp as humidity levels hit 100 per cent and moisture accumulates Forecasters say relief is in sight and humidity expected to start to drop after Wednesday morning

1. What is relative humidity and what does 100 per cent mean?

2. Why does Hong Kong get so humid during spring?

Advice on how to deal with damp as humidity levels hit 100 per cent and moisture accumulates

Forecasters say relief is in sight and humidity expected to start to drop after Wednesday morning