Explainer | What sparked 12,000 lightning strikes in Hong Kong in 1 morning and is your home safe?
- Lightning struck a flat in Wo Tin Estate, startling tenant and her daughter who were getting ready for school
- Typhoon Mawar influenced the region’s weather despite coming nowhere near Hong Kong
A storm on Thursday morning influenced by Typhoon Mawar resulted in more than 12,000 cloud-to-ground lightning strikes, with a public housing tenant in Tuen Mun having a first-hand encounter.
Lightning struck a flat in Wo Tin Estate when the amber rainstorm warning was in force. It is suspected of having peeled off part of the concrete on the outer wall. The Nepalese tenant, Gurung Preeti, said she saw a fireball and heard a loud noise while she was combing her daughter’s hair.
Although the Housing Department later said no indoor repairs were needed following investigations, the tenant said her daughter was so startled that she did not feel safe staying in the flat.
The Post looks into how the incident happened and how safe residents are in their own homes.
1. What caused so many lightning strikes?
Warmer air can capture more water molecules than cooler air, these droplets and ice crystals bump into each other and move apart during a storm, forming electric charges in the clouds.
There are three common types of lightning: cloud-to-ground, cloud-to-cloud and cloud-to-air.
A cloud-to-ground strike is the rarest and the most dangerous type among the three because it involves lightning coming to the ground instead of staying in the atmosphere.
It can be observed when the channel of electrically charged air stored in the cloud is discharged to the ground.
On Thursday morning, Typhoon Mawar, one of the most powerful storms worldwide so far this year, was located over 200km (124 miles) southwest of Okinawa, Japan’s southernmost prefecture.
Its influence was felt in Hong Kong and neighbouring regions. Since last Friday, it caused “persistently very hot” weather in Guangdong, according to The Hong Kong Observatory.
Its acting senior scientific officer David Lam Hok-yin said Thursday morning’s lightning was also an effect of the prolonged heat.
“Thunderstorms caused by high temperatures sometimes bring more and stronger lightning, although it doesn’t happen every time.”
2. Why are buildings susceptible to lightning strikes?
Buildings are highly susceptible to lightning strikes because they are usually taller than their surroundings. Their outer walls also remain wet after rain and become good conductors of electricity.
For example, the Empire State Building in New York is hit by lightning about 25 times annually, according to its website.
Lightning often strikes the same place, according to the National Oceanic and Atmospheric Administration, especially if it is a tall and isolated object.
The United States National Weather Service said a single bolt of lightning could heat the air it passes through to 50,000 degrees Fahrenheit (27,760 degrees Celsius), or five times hotter than the sun’s surface, causing significant fire damage to buildings without appropriate protection.
3. Why was the building struck by lightning despite having a lightning rod?
The lightning rod is placed atop a building to protect its structural integrity. It is made of highly conductive material, such as copper, and is connected to a wire that runs down to the ground.
It acts as a safe and effective path for lightning and its currents.
Registered engineer and mechanics expert Lo Kok-keung said the incident in Wo Tin Estate was rare and predicted that there could be a problem with the building’s lightning protection system.
“If the lightning rod is installed correctly, it must be working. After the electric current is attracted to the first and highest contact point, it is passed to the ground,” he said.
“The lightning protection wire is connected from the roof to the ground. It could have been damaged somewhere in the middle.”
4. What are the risks of being struck by lightning in urban areas?
Leung Wing-mo, former assistant director at the Observatory, said the individual lightning protection systems installed on each building collectively formed a shield in the city, so the risk of residents being struck in urban areas was low.
“I have never heard of any deaths and injuries from lightning strikes in the city. Those cases were mostly from the countryside or in the sea,” he said.
“When you are in the countryside, there will be no way to protect yourself other than staying vigilant and resigning yourself to your fate as a lightning strike is powerful and its course is random.”
The Observatory said that in case of an electric storm, residents could refer to its location-specific lightning nowcast to draw up contingency plans with an exit plan before hiking, such as altering the route or cancelling the trip if necessary.
“Watch out for weather changes and regularly review the chance of thunderstorms in the next couple of hours during the trip,” the weather forecaster said on its website.
Additional reporting by Emily Hung
