A cleanup operation is underway in Queensland, Australia, after Cyclone Debbie made landfall between Bowen and Airlie Beach on Tuesday 28 March 2017, leaving a trail of devastation about 50 km across. One man is in hospital with serious injuries following a wall collapse in Prosperine, and authorities are reporting a single known death, though they have not yet released any details of this, and have expressed fears that there may be further casualties in remote communities cut off by the storm. Around 25 000 people were evacuated from homes directly in the path of the storm, and about 48 000 homes have been left without power, with warnings being issued about the dangers of downed power lines. Flooding has been reported around Prosperine, and evacuees returning to their homes are being warned to expect extensive damage.
Trees being battered by high winds and rain at Arlie Beach as Cyclone Debbie passes. Reuters.
Cyclone Debbie is recorded to have been a Category Four storm as it made landfall, that is to say a storm with sustained windspeeds in
excess of 209 kilometers per hour (a sustained windspeed is defined as a
windspeed recorded continuously for periods in excess of a minute), though the storm has lost energy as it has passed over land, though high winds are expected in the area till at least Wednesday 29 March.
The passage of Cyclone Winston till 07.00 GMT on Tuesday 28 March 2017 (thick
line) with its predicted future path (thin line, circles represent the
margin of error on the predictions). Colours indicate the strength of
the storm. Tropical Storm Risk.
Tropical
cyclones are caused by solar energy heating the air above the oceans,
which causes the air to rise leading to an inrush of air. If this
happens over a large enough area the inrushing air will start to
circulate, as the rotation of the Earth causes the winds closer to the
equator to move eastwards compared to those further away (the Coriolis
Effect). This leads to tropical storms rotating clockwise in the
southern hemisphere and anticlockwise in the northern hemisphere.These
storms tend to grow in strength as they move across the ocean and lose
it as they pass over land (this is not completely true: many tropical
storms peter out without reaching land due to wider atmospheric
patterns), since the land tends to absorb solar energy while the sea
reflects it.
View of Cyclone Debbie from the International Space Station. Force 13.
The
low pressure above tropical storms causes water to rise there by ~1 cm
for every millibar drop in pressure, leading to a storm surge that can
overwhelm low-lying coastal areas, while at the same time the heat leads
to high levels of evaporation from the sea - and subsequently high
levels of rainfall. This can cause additional flooding on land, as well
as landslides.
See also...
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