Typhoons 101

Typhoons 101

31 August, 2016
Storm season is here!
How much do you really know about Hong Kong’s climatic hazard?

As we head into typhoon season, with Typhoon Nida kicking things off in fine ‘Signal 8’ form earlier this month, we thought it might be interesting to learn a little more about this weather phenomenon that is part of life in our corner of the world. You’re welcome!

How do typhoons form?

Typhoons rely on warm ocean waters to fuel their formation. This is why they only form near the equator. Because the temperatures are warmer, it allows warm, moist air to rise and this condenses to form clouds. This leaves an area underneath that has less air, and so low pressure. This area of low pressure ‘sucks’ in air from nearby warm surroundings, and this continues to fuel cloud and rain formation. The rotation of the earth then causes this system to rotate (anti-clockwise in the northern hemisphere, clockwise in the southern hemisphere). This phenomenon is called the Coriolis effect.

Air is then ejected at the top of the storm, and falls over and out of the storm. This creates the characteristic ‘eye’ of a typhoon. The reduction of mass at the centre of the ‘eye’ lowers the pressure and causes wind speed to increase.

What’s the difference between a typhoon, cyclone and hurricane?

The physical characteristics are all the same thing! The only factor that separates them is their physical location. Hurricanes are those formed over the Atlantic Ocean or eastern Pacific Ocean. Cyclones are those developed in the Bay of Bengal and the Arabia Sea. Typhoons are those formed in the Northwest Pacific Ocean. A tropical cyclone is a generic term used to describe all three.

When was the last T10 in Hong Kong?

The last typhoon no.10 signal that was raised in Hong Kong was back in 2012, when Typhoon Vincente brought maximum wind speeds of 140 km/h, and a storm surge of about 1.5 m. This marked the first time that the T10 signal had been hosted since the 1999 Typhoon York, which killed two people.

Are typhoons getting worse?

This is a pressing multi-million dollar question, and one that has yet to reach a scientific consensus.

As discussed above, typhoons rely on warm sea surface temperatures to drive their power. It seems logical that warming ocean temperatures means more typhoons. However, warming seas also cause an increasing in the strength of shearing winds (winds blowing in different strengths and directions and different altitudes). These winds hinder the formation of typhoons, or tear them apart.

In recent years, there have been above-normal sea surface temperatures over the central and eastern equatorial Pacific. The result of this is that the breeding ground of typhoons is being displaced further east. The impact of this is that typhoons formed further east will spend a greater amount of time over oceans, thus increasing the chance for them to develop into super typhoons.

So, while it’s unclear at the moment whether the frequency of typhoons are on the rise, it’s been found that the intensity of storms is certainly increasing.

Batten down the hatches.

By: Ecozine Staff


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