Sunday 25 August 2019

Tropical Storm Bailu kills at least three as it sweeps across the Philippines and Taiwan.

Three people are now known to have died as Tropical Storm Bailu swept across the Philippines and Taiwan this week. A seventeen-year-old girl was killed when her house was demolished by a landslide triggered by the storm in Ilocos Norte Province, the Philippines, with two other children injured in the incident, while in the same province a 37-year-old man drowned after being trapped by floodwaters in Laoag City. The storm caused a series of other landslip and flooding events across the northern Philippines before making landfall in Taiwan, where an eighteen-year-old motorcyclist died following a collision with a tree felled by the storm, and several more people were injured in storm-related incidents. The storm made landfall in Fujian Province, China, at about 7.35 am on Sunday 25 August 2019, bringing with it 10-12 cm of rainfall in a few hours, and winds of up to 75 km per hour, though there are no reports of any casualties, largely due to the evacuation of around 50 000 people from the immediate path of the storm.

Flooding in the town of Burgos in Ilocos Norte Province, the Philippines, following the passage of Tropical Storm Bailu this week. Eagle News.

Tropical storms are caused by the warming effect of the Sun over tropical seas. As the air warms it expands, causing a drop in air pressure, and rises, causing air from outside the area to rush in to replace it. If this happens over a sufficiently wide area then the inrushing winds will be affected by centrifugal forces caused by the Earth's rotation (the Coriolis effect). This means that winds will be deflected clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere, eventually creating a large, rotating Tropical Storm. They have different names in different parts of the world, with those in the northwest Pacific being referred to as typhoons.

The path and strength of Tropical Storm Bailu. Thick line indicates the past path of the storm (till 6.00 pm GMT on Sunday 25 August 2019), while the thin line indicates the predicted future path of the storm, and the dotted circles the margin of error at 12 and 24 hours ahead. Colour indicated the severity of the storm. Tropical Storm Risk.

Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.

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