Swirling Force of Nature
Cyclone Fani just battered Odisha on India’s east coast and Bangladesh killing 66 (as of 9 May 2019), damaging property worth $72.8 billion, and throwing life out of gear. About five years ago, Cyclone Phalin had ravaged roughly the same areas.
Speak of hurricanes and the haunting memories of Katrina and Sandy come back flooding – literally and figuratively. When they hit habitations, tropical cyclones leave behind a trail of death and devastation.
| Region | Name for Tropical Cyclone |
| Indian Ocean | Tropical Cyclone |
| North Atlantic Ocean and East Pacific Ocean | Hurricane |
| West Pacific Ocean | Typhoons |
| Australia | Willi-Willi |
Table 1. Names for Tropical Cyclones in Different Regions
So, what is a cyclone? How are cyclones / hurricanes formed? How do they move from sea to land? And why do they destroy anything and everything that dares stand tall in their path?
Tropical Cyclone Formation
Cyclones are a wind mechanism that rotates anti-clockwise in the northern hemisphere and clockwise in the southern.
Conditions which cause about 95% of cyclones are intense heating of sea surface water at minimum 26.50C (79.70F) temperature and at least 50m (160 feet) depth. Sufficient depth supplies the required amount of water and high temperature evaporates water in ample quantity.
In the first stage of tropical cyclone formation, moist and warm air at low pressure rises and diverges forming a low-pressure ‘eye’ at the center. Next, cool air at high pressure gushes in from the neighboring areas creating a system of inward spiraling winds that gets heated up. The cycle continues. Warm, wet air forms clouds as the entire system expands and spirals upwards at growing speed.
| Category of Tropical Storm | Wind Speed (miles per hour) |
| Weak -1 | 75-95 |
| Moderate – 2 | 96-110 |
| Strong – 3 | 111-130 |
| Very Strong – 4 | 131-156 |
| Devastating – 5 | Above 156 |
Table 2. Saffir-Simpson Scale on Hurricane Intensity
Winds with strong vertical gradient deny time for the system to build up momentum – the reason why there are virtually no hurricanes in the South Atlantic. Next, earth’s rotation speed lends them the rotating swirl. Slow rotation speed near the equator means cyclones do not usually form 5 degrees north and south of equator.
Movement
Tropical cyclone trajectories can be confusing on account of the multiple driving forces. Usually, they move with the prevailing winds – from east to west with the trade winds in the tropics. Coriolis Force moves them pole-wards. A tropical cyclone may also interact with other cyclones or the jet stream and change its direction.
Devastation
Torrential rains, storm surge, and catastrophic winds are a hurricane’s three agents of destruction. Rains can hit 2.5cm (1inch) per hour while storm surge raises sea levels, both of which crate floods and turbulent streams even as galloping winds uproot homes, trees, electricity poles, and what not.
| Feature | Statistic |
| Cyclone Diameter | 100-2000 km (62-1243 miles) |
| Eye Diameter | 30-65 km (20-40 miles) |
| Duration | 5-10 days |
| Distance Travelled | 800 km (500 miles) per day |
Table 3. Hurricane Statistics
Rotating around the calm eye of the hurricane is the violent ‘eye wall’ that houses the three agents of disaster. If you are in the path of a cyclone know this: There will be two rounds of stormy rains, one from the eye wall ahead of the eye and another from the trailing eye wall. Don’t let down your guard after surviving the first!
Weakening & Death of Cyclone
When hurricane moves to cooler land or water, the heat source which creates and sustains it is no longer available and it dies away. Hurricanes may converge cold and hot air. Cold air pushes up and swirls the hot air to form a funnel cloud, popularly called a tornado.
Hurricanes & Global Warming
Although it appeared late in the North Atlantic hurricane season, Hurricane Sandy surprised everyone by killing 233 and inflicting $68.7 billion (2012) in damages in October-November 2012.
With global warming heating up the planet, sea surface temperature is climbing upward and providing the necessary (if not sufficient) condition for cyclone formation. The frequency, intensity, and distance traveled by cyclones before dissipating are all surging.
However, scientists are also improving weather forecast and better predicting hurricane trajectories. There are live cyclone trackers as well. Such developments have minimized damage to life and property. Forewarned truly is forearmed. But then, prevention (of global warming) is better than cure! Moving ahead, we need a bit of both.
Indrajeetsinh Yadav @ Falcon Words has composed this article. Falcon Words offers stellar content on environmental issues. Write to us at info@falconwords.com or call us at +91-9822052945 for content tailored to your specific requirements.