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In the year 2016, Typhoons made a late appearance in Japan. It ranked as the second-latest occurrence in recorded statistics for this country.
While a lack of typhoon is much to the delight of divers, this extended absence led to a rise in sea temperature. This usually causes widespread coral bleaching events.
In 2017, we saw the formation of three typhoons in early July.
In 2018, we observed a notable increase in the frequency of the term “typhoon” in weather forecasts.
For divers, typhoons present themselves as formidable challenges.
You may already know that some typhoons are less intense while others pack a more powerful punch. Therefore, this time, we’ll be providing a guide to comprehending the various intensities of typhoons.
Understanding Typhoon Intensity
The strength of a typhoon is measured in units of hPa (hectopascal), which quantifies atmospheric pressure.
You may already be familiar with terms like low-pressure and high-pressure systems. In simpler terms, when a low-pressure system approaches, it brings rainfall. When a high-pressure system approaches it leads to clear weather.
Air naturally moves from areas of higher pressure to lower pressure. This causes winds to converge towards the center of the low-pressure system.
This convergence triggers the formation of updrafts and subsequently results in cloud development.
In meteorology, it’s important to note that terms like ‘high’ and ‘low’ pressure are relative to the surrounding atmospheric pressure, despite 1 atmosphere equating to about 1013 hPa. This means encountering a low-pressure system with higher pressure than 1 atmosphere (1013 hPa) is common.
Now, let’s explore the concept of typhoons. Essentially, they resemble eerie low-pressure systems. A typhoon earns its title when the maximum average wind speed within a low-pressure system exceeds 17 m/s. It’s crucial to mention that a key defining factor is the presence of this low-pressure system in the northwestern Pacific or South China Sea.
Due to their lower atmospheric pressure compared to typical ones, typhoons exhibit a more pronounced pressure contrast with their surroundings. This prompts a greater influx of air towards the typhoon’s center.
The result is powerful winds and intense rainfall. The greater the contrast in atmospheric pressure with the surrounding area, the more potent the typhoon’s force.
Assessing Typhoon Intensity
Understanding a typhoon’s strength involves more than just its atmospheric pressure. It’s also about the contrast with the surrounding pressure. While this isn’t the sole factor, paying attention to the pressure at the center can provide a general indication.
As a rough guide:
- 990 hPa and higher: Classified as weak
- 960 hPa to 990 hPa: Falls within the typical range
- 930 hPa to 960 hPa: Indicates considerable strength
- 930 hPa and below: Signifies a powerful typhoon
It’s important to remember that terms like ‘strong’ or ‘violent’, used by some Meteorological Agencies, are based on wind speed. They might not align exactly with these benchmarks. Keep this in mind.
Regardless, even a weak typhoon can result in localized damage. So, if you find yourself in an affected area, maintaining vigilance is crucial!
Memorable Past Typhoons
The year 2015 saw the arrival of Typhoon 21, named Dujuan. Its impact was unforgettable. It was observed with a momentary peak wind speed of 81.1 m/s on Yonaguni Island. Eyewitnesses claimed to have seen taxis airborne.
At the height of this typhoon, the lowest recorded atmospheric pressure near Yonaguni Island plummeted to 949.3 hPa. Interestingly, the strongest wind happened a little later, when the air pressure had gone up a bit.
The Isewan Typhoon: Unprecedented Devastation
In 1959, Typhoon 15 (known as Typhoon Vera) remains etched in history as Japan’s most catastrophic natural disaster.
The toll was measured not only in terms of lives lost but also in the economic losses. It is said to rival with the devastation caused by the Great Kanto Earthquake in 1923 and often drawing parallels to the impact of the Tohoku Earthquake in 2011.
This typhoon made landfall with a central pressure of 930 hPa, squarely placing it in the ‘violent’ category.
Upon examination of many other typhoons, it was clear that the ones causing a lot of damage were the ones classified as “Strong” or above.
For divers like us, the impacts are felt well in advance of a typhoon approach. The more robust the winds, the higher the waves escalate in the local area.
These waves transmute into swells that directly affect us. Thus, it is of utmost importance to track the typhoon’s strength long before it reaches the shores and to maintain a vigilant eye on sea conditions!
