At least 35 killed and 17 missing after Typhoon Hagibis tears through country, flooding rivers and submerging cities. —Satoshi Sugiyama, Japan Times 13 October 2019
by Roger Childs
The season in Japan
It is that time of the year – late summer in the Northern Hemisphere – when these weather bombs are spawned. They always cause considerable damage, but Hagibis is one of the worst since records have been kept in Japan.
- Many people have died and been injured.
- Property and settlements have been destroyed.
- Rivers have broken their banks flooding wide areas.
- Some places have received their highest rainfall ever.
Obviously we are more interested in the tragedy this time because of the World Cup taking place in the country, but it important to get things in perspective. Rugby in the end is only a game and a few match cancellations are nothing compared with the loss of life, houses destroyed and transport disrupted. The apoplectic comments from the Scottish rugby administrators about possibly missing out on playing Japan were very selfish and highly insensitive.
What creates a typhoon?
Typhoon is the Japanese term for what we call a (tropical) cyclone and the Americans call a hurricane. Tropical is the key word as these massive low pressure systems originate within a few degrees of latitude near the Equator. High sea temperatures are the source of typhoons, and in the late summer the oceans in the tropics reach a heat ideal for spawning the storms. The paths of typhoons are difficult to predict, however the formation process follows a set pattern.
Here is the recipe.
TAKE 1 A large warm ocean area
ADD 2 Storms developing on the edge of the Inter Tropical Convergence Zone where trade winds from the two hemispheres interact
ADD 3 Air sucked up into the upper atmosphere, sometimes aided by the jet stream
THEN 4 Stir with the Earth’s rotation – the Coriolis Force (this give the typhoon its characteristic swirl shape)
THEN 5 Add heat given off by condensation of water in the air.
Typhoons / hurricanes / tropical cyclones need an on-going supply of energy from warm seas to keep them going. In Japan’s case the warm Kuroshio Current provides this fuel. It flows north-east from the South China Sea and passes south of the Japanese islands. Off the coast of the United States the Gulf Stream serves the same function.
Typhoons only travel at about 25-35 km/h, but the winds that swirl around the calm eye of the storm may reach over 300 km/hr. These intense low pressure systems rotates anti-clockwise in the Northern Hemisphere and clockwise in the Southern.
A typhoon will lose its strength when it passes over land or across colder waters, however it will continue to pack a punch for some time after hitting the coast.
Typhoons are massive hazards as they bring a cocktail of appalling weather and impacts on the land.
- Very strong winds which cease for a short time as the eyes passes over.
- High seas and large waves driven by the winds.
- Torrential rain which invariably causes flooding and landslides.
- Storm surges which result from a temporary rise in sea level where the ocean waters are literally pulled up by the rapidly rising air in the low pressure system.
The results of these factors, as exhibited by Hagibis are loss of life; widespread damage to property; flooding of settlements, transport systems and farmland; damage to crops, trees and stock. Not surprisingly, areas close to the coast are most vulnerable to the devastating impact of typhoons.
For the areas affected there is then the huge job of cleaning up and rebuilding.