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IMD’s Cyclone Prediction Involves Lengthy Observations, Numerical Models, Building Consensus

There are many procedures for cyclone warning and with the advent of technology, the task of monitoring and predictions has improved.


Updated:May 3, 2019, 6:56 PM IST
IMD’s Cyclone Prediction Involves Lengthy Observations, Numerical Models, Building Consensus
Representative image.

New Delhi: There are multiple numerical models, mathematical equations, statistical data and consensus building required before issuing the cyclone warning or predictions.

As Cyclone Fani rips through Odisha with rain and thunderstorm, leaving at least six people dead, News18 explains how cyclones are predicted.

Several Procedures

In 1865, the cyclone warning system was organised for the first time, which was followed by the establishment of the India Meteorological Department (IMD) in 1875.

There are many procedures for cyclone warning and with the advent of technology, the task of monitoring and predictions has improved.

It requires good observational network, including satellites, stations and meters, to provide data on sea and land.

Since cyclone develops in the sea, the use of strata meters is the basic requirement. There is a basic programme in place with which the IMD monitors and detects cyclones.

Warning happens before the existence of a cyclone. “The observations made in stations are invested into making the numerical weather prediction models,” Mrutyunjay Mohapatra, IMD Scientist, Head of the cyclone department told News18.

Observations Drawn at IMD Become Models

The observations are made into numerical weather prediction models. Through tie-ups with other countries, the information is collated and analysed. IMD refers to 10 different numerical models every day. These models ingest the current observations and are applied in different physical principles and mathematical equations.

With the help of high-powered computing systems, experts solve these equations and analyse it for actual observation. The prediction is then made for different days.

Forecasters go through all these models that are developed every day to find out whether any low pressure system is developing anywhere in the sea. Once such a detention takes place, scientists go ahead with their predictions.

Building consensus

One of the most important tasks is ‘building consensus’. The models developed through different observations are not uniform in nature and do not agree with each other, which is just like doctors differing over an ailment. “As a result, it becomes difficult to draw a conclusion,” Mohapatra added.

Finally, all the scientists interface all these models with the help of their knowledge, experience and expertise. To reach a consensus over the models, meteorologists confer with each other. There is a video conference every day to bring about a consensus over the forecast.

Statistical techniques are used to reach the consensus from the models. “Forecasters differ over the models, so through video-conferencing, differences are ironed out and a final forecast is generated,” he said.

After the forecast is decided, the information is disseminated by cyclone warning centres.

The centres issue 13 types of bulletin, catering to different kinds of users — railways, press, force, shipping and so on. The forecast is then converted into user-friendly, plane language bulletin, along with graphic presentation.

This early warning bulletin in the first stage is issued by the Director General of Meteorology and is addressed to the Cabinet Secretary and other senior government officers, including the chief secretaries of the coastal states concerned.

Special warnings are issued for fishermen four times a day during normal weather, and every three hours in case of disturbed weather.

The general public, coastal residents and fishermen are warned through state government officials and broadcast through All India Radio and national television (Doordarshan).

4-Stage Warnings for States

The first-stage warning known as “Pre-Cyclone Watch” is issued 72 hours in advance. It contains early warning about the development of a cyclonic disturbance in the north Indian Ocean.

The second-stage warning is known as “Cyclone Alert”, which is issued at least 48 hours in advance of the expected commencement of adverse weather over the coastal areas.

It contains information on the location and intensity of the storm, likely direction of its movement, intensification, coastal districts likely to experience adverse weather and advice to fishermen, general public, media and disaster management agencies.

This is issued by the area cyclone warning centres (ACWCs)/cyclone warning centres (CWCs) and cyclone warning division (CWD) concerned.

The third-stage warning, known as “Cyclone Warning”, is issued at least 24 hours in advance of the expected commencement of adverse weather over the coastal areas.

Landfall point is forecast at this stage. These warnings are issued by the ACWCs/CWCs/and CWD at three-hour intervals giving the latest position of the cyclone and its intensity, likely point and time of landfall, associated heavy rainfall, strong wind and storm surge along with their impact and advice to general public, media, fishermen and disaster managers.

The fourth stage of warning known as “Post-Landfall Outlook” is issued by the centres at least 12 hours in advance of the expected time of landfall. It gives likely direction of movement of the cyclone after its landfall and adverse weather likely to be experienced in the interior areas.

Different colour codes are also used to denote the different stages of the cyclone warning bulletins.

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