Why India needs cyclone warning
The India Metrological Department (IMD) under the Ministry of Earth Sciences (MoES), encountered professionally eventful 2016 with Vardah—a cyclone that brought life in Chennai to a standstill for several days and several other tropical cyclones formed over the Indian seas in the later half of the year. Tropical cyclone Kyant saw fishermen being cautioned from venturing into the deep waters of South coastal Andhra Pradesh while Nada passed off Karaikal Coast in Puducherry peacefully (Fig 1).
Early cyclone warning becomes crucial at all such events. The components include effective monitoring, detection and prediction of tropical cyclones, followed by coordination with state level emergency response systems. Most importantly, educating the public about the credibility of official warnings and disseminating information timely to them is vital. Critical prediction of associated adverse weather such as heavy rain, gale wind, high waves, storm surge and coastal inundation form the basis for forecasting the impacts. The typical satellite and radar imageries of these tropical cyclones (TCs) are shown in figure 1. The best track of these TCs and characteristic features are shown in figure 2.
Monitoring and forecasting
There are several problems which are encountered while predicting cyclonic systems. Cyclones often change their course (recurving) and head in the opposite direction besides weakening and fizzling out, or intensifying when least expected. Considering these difficulties in the prediction of cyclones, the analysis and decision-making process had to be made by blending scientific advancements, dynamical and statistical models, meteorological datasets, technology and expertise.
A decision support system (DSS) in a digital environment was used to plot and analyse different weather parameters, satellite and radar and numerical weather prediction (NWP) model products. In this hybrid system, synoptic wisdom could get overlaid on NWP model products supported by modern graphical and geographical information system (GIS) applications which could produce quality guidance for decision. Also, forecasting tracks up to 120 hours, its uncertainty and wind movements in different sectors of the tropical cyclones is a challenge. Thus, additional help is usually sought from the regional offices, national and international centres to collect and analyse radar data and products from IMD’s radar network, satellite imageries.
Ocean state monitoring and forecasting of tropical cyclones
Better observational tools such as buoys and ships deployed over the Bay of Bengal, provided the sea surface temperature and tropical cyclone heat potential, which have been recently made available from Indian National Centre for Ocean Information Services (INCOIS), Hyderabad. It helped in assessing the possible intensification/weakening trends of tropical cyclones as well as their genesis and track characteristics. This information coupled with the guidance available from global and regional atmospheric numerical models helped in better forecasting of unusual behaviour of tropical cyclones and cyclone warning.
Performance evaluation of cyclone warning forecasts
The errors that occurred while predicting the three tropical cyclones in 2016 was less in comparison to the average errors of the last five years even though the tracks were recurving. Considering the intensity forecasts, the errors were less in intensity forecasts in terms of maximum sustained wind speed. Landfall point forecast errors were also less which had led to lesser number of people being evacuated. An example of the accurate landfall, track and intensity forecasts 36 hrs in advance in case of cyclone, Vardah is shown in figure 3.
The timely and accurate forecast of IMD not only led to minimum loss of lives and smaller area of evacuation during the tropical cyclones, but also resulted in an enhanced confidence in disaster managers. Though there has been significant improvement in the recent years, there is still scope for further improvement. Various initiatives such as forecast demonstration projects, aircraft probing, augmentation in observational network, introduction of ocean atmosphere coupled high resolution regional model and operationalisation of ensemble prediction system for probabilistic forecast products are being attempted for further improvement of cyclone warning services.
Regional Specialized Meteorological Centre. 2016. Press Release Dated: 11-12-2016.
The author is Director General of Meteorology, India Meteorological Department. email@example.com