Cyclone- A nature's fury

Audio Version of article given above.

W

e witnessed Super Cyclone storm Amphan (pronounced Um-pun) in the Eastern parts of India recently. It made a landfall by hitting West Bengal (India) on 20^th May 2020.

In this article I will try to discuss about cyclones.

Types of Cyclones

The term ‘cyclone’, meaning, ‘coil of a snake’ was coined in Calcutta by Henry Paddington, an English merchant captain who settled in Bengal. He wrote many papers on Tropical storms.

A cyclonic storm is caused by blowing of wind over sea/ocean due to fall in atmospheric pressure in that area as compared to the same in the surrounding areas.

Cyclones are of two types:

a)  Synoptic: In simple words, this type of cyclone moves horizontally to the extent of 1000 Km. or more.

A Tropical Cyclone is a synoptic low-pressure disturbance in the tropical oceans.

The other two types of Synoptic cyclones are Extratropical and Subtropical.

b)  Mesocyclone: As opposite to the Synoptic Cyclones, Mesocyclones move vertically and mainly have a curling wind formation. For example, a tornado is a type of Mesocyclone.

Stages of Cyclone Warning in India

The cyclone warnings are issued by state governments in four stages:

a)  Pre-Cyclone Watch: It is the First Stage warning. It is issued 72 hours in advance of the expected start of bad weather. It contains early warnings about the development of cyclonic depression and its possibility of becoming a cyclonic storm.

b)  Cyclone Alert (Yellow Message): It is the Second Stage warning. It is issued 48 hours in advance. It contains the information about areas to be affected, intensity and movement of the bad weather. It also contains advice to fishermen and the general public.

c)  Cyclone Warning (Orange Message): It is the Third Stage warning. These are issued 24 hours in advance, at an interval of every three hours. Each time giving latest information about the position and intensity of the bad weather and its impact on the general public. The expected point and time of landfall is announced in this stage.

d)  Post Landfall Outlook (Red Message): It is the Fourth Stage Warning. It is issued 12 hours in advance of expected landfall time. It contains the information about the expected path of the cyclone after landfall.

For the ports, 11 level Storm Warning Signals are issued by Cyclonic Warning Centers. They are hoisted on the port authorities at the affected ports.

Similarly, for the Indian Navy, Fleet Forecasts are issued by IMD.

Coastal Bulletins are issued by IMD for coastal areas upto 75 Km. from the coastline.

Sea Area Bulletins are issued by IMD for sea beyond 75 Km.

Categories

The Indian Metrological Department (IMD) makes the following classification of  weather phenomena, based on the wind speed:

i)               Depression: Wind speed at surface between 17-27 Knots (Approx. 31-50 Kmph)

ii)             Deep Depression: Wind speed at surface between 28-33 Knots (Approx. 51-61 Kmph)

iii)           Cyclonic Storm: Wind speed at surface between 34-47 Knots (Approx. 62-87 Kmph)

iv)           Severe Cyclonic Storm: Wind speed at surface between 48-63 Knots (Approx. 88-117 Kmph)

v)             Very Severe Cyclonic Storm: Wind speed at surface between 64-89 Knots (Approx. 118-166 Kmph)

vi)           Extremely Severe Cyclonic Storm: Wind speed at surface between 90-119 Knots (167-221 Kmph)

vii)         Super Cyclonic Storm: Wind speed at surface being 120 Knots and above (Approx. 222 Kmph and above)

In USA a different  scale called SSHWS (Saffir-Simpson Hurricane Wind Scale) is used. It divides the wind speeds into 5 categories: Category One being with wind speed between 119-153 Kmph to Category Five being with wind speed above 252 Kmph.

Amphan had touched a speed of 255 Kmph so it is designated as Super Cyclonic Storm or Category Five Cyclonic Storm.

Nomenclature of Cyclones

We  know every cyclone is given a different name. These names are regulated by the World Metrological Organisation (WMO), an agency of the UNO, working on international cooperation between member countries in the areas of earth’s atmosphere, weather, land & oceans and resulting distribution of water resources.

These names are given for easy recognition of the cyclones in the warning messages.

Since 1953, the names of cyclones in a particular area are decided by the panel of member countries for that particular region from a list containing names of the member countries in alphabetical order in one column and the proposed names for cyclones, given in the second column.

For example, India is a member of the 13-member panel (WMO-ESCAP)  responsible for naming the cyclones occurring in the Arabian Sea and the Bay of Bengal. Regional Specialised Monitoring Centre of IMD, GoI (RSMC, New Delhi), acts as headquarters for this panel.

The name ‘Amphan’, given by Thailand was taken as it was unused till now. It was the last name in the current list. After ‘Amphan’, new list will begin and the next name for a cyclone in this area will be ‘Nisarga’, given by Bangladesh.

Hurricane, Typhoon and Cyclone

It is interesting to note that Hurricane, Typhoon, and Cyclone are different names of the same weather phenomenon. The name depends on the location of its occurrence.

Hurricane occurs in eastern & central parts of North Pacific, North Atlantic Ocean, Caribbean Sea and Gulf of Mexico.

Typhoon occurs in western North Pacific Ocean.

Cyclone occurs in the Arabian Sea and Bay of Bengal.

Tropical Cyclone occurs in South Pacific and southwest Indian Ocean.

Cyclone Amphan

Cyclone Amphan that made landfall in India on 20^th May 2020 in West Bengal was the first Tropical Cyclone of 2020 in the North Indian Ocean.

Ø On 16^th May 2020 IMD designated it as a Depression, then Deep Depression but the wind speed kept on intensifying. It was designated as a Cyclonic Storm at 5.30 PM IST and was named Amphan.

Ø By 17^th May 2020 the wind speed had rapidly increased further and it was designated as Severe Cyclonic Storm and later as Very Severe Cyclonic Storm.

Ø On 18^th May 2020 2.30 PM IST, it designated the storm as Super Cyclonic Storm.

Ø On 19^th May 2020, 11.30 AM IST the storm was downgraded to Extremely Severe Cyclonic Storm.

Ø On 20^th May 2020, the cyclone made a landfall at Digha, West Bengal though before the landfall its intensity further downgraded to Very Severe Cyclone.

Ø By 21^st May 2020, the cyclone degraded further and dissipated as a Depression.

It affected parts of West Bengal Odisha and Kerala in India and also Sri Lanka and Bangladesh. Around 4.2 Million people were evacuated in India and Bangladesh combined despite the ongoing pandemic. Trains were stopped in Odisha and West Bengal. Since high wind speed was expected, train coaches were tied to ground with chains in the yard of Howrah Railway Station. The operations at Kolkata Airport was stopped on 20^th May 2020, as a precaution against the cyclone.

We must appreciate that India has made technological advancements in metrology. Despite having a Super Cyclonic Storm (Category Five Cyclone) the death toll in all the three countries is only 118. Though every life is precious but we should appreciate that the number is extremely low as compared to the destruction caused. It is estimated that Amphan has caused a loss to the extent of $13 Billion.

The evacuations, saving a large number of lives, could be done timely because of continuous monitoring by extensive Doppler Weather Radar (DWR) network of IMD and India’s weather monitoring satellite INSAT 3D. IMD has 27 DWRs across India. India shared the information about the status of Amphan with other  WMO panel member countries in this region. Amphan was monitored by DWR in Vishakhapatnam and later on by DWR in Kolkata.

On one side such furies of nature can cause mass destruction, on the other side, the technological advancements keep saving the mankind.

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