This week’s catastrophic Philippines typhoon grew from a tropical storm to full-blown humanitarian disaster, devastating those unlucky enough to be trapped in its deadly path.
Typhoon Haiyan is thought to have killed 2275 people and injured 3655, with a further 80 still missing. International aid efforts are in full swing to manage the clean-up and stop disease spreading.
Although this storm reached unprecedented levels of destruction, about 20 cyclones pass through the Philippines each year. In fact, the area is renowned as ‘ground zero’ for storms of this kind. When Haiyan hit the central Philippines it was travelling with wind speeds of 313 kmh, but had gusts of up to 378 kmh, the strongest ever recorded.
The right conditions
So how does a storm of that catastrophic intensity develop?
All typhoons begin as a dangerous tropical storm. A super typhoon, like Haiyan, means the wind speeds are twice as powerful as the point where the storm became a typhoon. To become that destructive, a set of weather conditions must align.
The first ingredient needed to create a ferocious storm like Haiyan was warm ocean temperatures, explained Flinders University Meteorology lecturer Caecilia Ewenz.
“Usually a tropical cyclone, they form at least five degrees away from the equator and not much more than 20 degrees away,” Ms Ewenz said.
“Why is that? It needs warm ocean temperatures. Generally we say the sea surface temperature has to be above 26 degrees Celcius. That’s what the studies, the signs have shown in the past.”
Cyclones won’t form at the equator because they also rely on the earth’s gravitation to “get the right spin”.
The third condition was the wind direction and speed at different levels of the atmosphere.
Bureau of Meteorology duty forecaster Stuart Coombs said in this case there was little variation through the levels, creating a “well organised” beast.
“As it was approaching the Philippines there was less than five knots sheer or what we call change in wind speed with height across the depth of the steering winds of this system, so it was able to retain a vertical structure and a clean eye,” Mr Coombs said.
“So the low at the surface is drawing air in, which then rises in all the thunderstorms around the periphery of the eye and feeds the high pressure at the top which then throws the air outward from the centre in all directions.”
‘Like a tsunami’
While the cyclone itself is likely to cause damage, in many cases, like in the Philippines now, the greatest danger is the storm surge.
Haiyan was particularly dangerous because it was travelling at a high speed. While the winds were up to 313 kmh, the storm mass itself was travelling at 40 kmh.
Bureau of Meteorology duty forecaster Stuart Coombs said this created a “tsunami-like” mass of water which hit the land.
“In this event its been reported that sea levels might have risen between five and 10 metres as the super typhoon crossed the coast,” he said.
“It’s almost a bit like a tsunami. You get this huge body of water being forced on land and then on top of that, breaking waves that the wind generates. So you’ve got a double hit and that can act to bulldoze its way through coastal towns.”
Ms Ewenz said the pattern of the typhoon can also be deadly.
“The eye is where you have no wind or weak wind, when the wind comes again the direction of the wind is 180 degrees to what it was, so when you have so much damage from your cyclone already, it’s more or less the rubbish that flew away, now comes back after the eye has passed.”
Referencing a US-based National Oceanic and Atmospheric Administration study, Ms Ewenz said it was “devasating” what flying debris like a piece of corrugated iron roofing can do.
The Philippines has about 20 cyclones a year, which Coombs said was because the main factor was warm ocean temperatures. The area has some of the warmest waters in the world. It also meant that it could lull residents into a false sense of security despite early predictions.
“The Philippines are really unfortunately ground zero for a lot of these storms. It could well be that the people in the community thought it was just another typhoon and didn’t get too worried about.
“If you only catch the edge of a few you think, ‘Oh, they are not too bad’ until something like this takes a direct hit and there’s very little left after something like this hits with this intensity.”
Early predictions are not always possible. A small change in wind can mean the typhoon moves 80-100 km in a different direction, which can mean the difference between no danger and a direct hit on a town.
“In this case it wasn’t an issue it was just a matter of how intense of it got before it got to the Philippines.
“Well ahead of time it was pointed out that it was likely to become a super typhoon but you can’t really predict it will become the biggest super typhoon to hit land of all time.”