Decoding Mumbai's weather: The science behind forecasting and its complex challenges

Nestled on India's western coast, the bustling metropolis of Mumbai is known for its vibrancy, fast-paced life and rains. There's a vast collection of media and literature that has romanticised Mumbai rains. However, whenever the city is lashed with heavy rains, the challenges for the residents increase manifold as they have to deal with flooding, public transport disruptions and massive traffic jams.

Since flooding and traffic interruptions, therefore precise weather forecasting is critical for the city's residents and infrastructure.

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The monsoon is caused by a seasonal reversal in wind patterns, with moisture-laden winds from the Indian Ocean blowing over the subcontinent. Mumbai, due to its unique geographical location, is frequently subjected to heavy rainfall. However, predicting when and how these rains will fall is not a simple undertaking.

It is an endeavour that requires advanced equipment, intricate methodology, and a thorough understanding of atmospheric dynamics. The most important of them all are the scientists who analyse the data to present the most accurate forecast for the public.

Mid-day.com spoke to scientists of the India Meteorological Department's regional centre in Mumbai to understand the process behind weather forecasting.

Speaking to the newspaper, Sunil Kamble, director of IMD Mumbai, said that the scientists keep monitoring the weather physically at three-hour intervals as suggested by the World Meteorological Organisation. Kamble added that additionally, they receive data from automatic weather stations at 15-minute intervals.

"In today's day and age, almost all departments including aviation require weather forecasting. In the Mumbai airport's Air Traffic Control Room alone IMD has 80 officers who constantly monitor the city's weather. The scientists don't just analyse the readings obtained through the local tools to issue a forecast for Mumbai but also have to take into consideration the global weather conditions and what impact it will bear on the city," Kamble explained.

He added that the scientists also have to gauge the impact of weather systems across India and rely on the climatology of a particular area while issuing a forecast.

"Even when we issue a forecast, it is a possibility and not an absolute fact," he chimed.

Technologies in weather forecasting

The tools used in weather forecasting by the IMD are satellite imagery, doppler radar systems, automatic rain gauges and automatic weather stations, Kamble said and added that apart from these tools, the weather agency relies on radiation instruments, ships and flights.

Satellites orbiting the Earth give real-time information on cloud formations, sea surface temperatures, and atmospheric conditions. These satellites transmit data to ground stations, which meteorologists use to forecast rainfall, storm systems, and other weather occurrences.

Doppler radar systems emit radio waves that bounce off raindrops, providing precise information about the location, intensity, and movement of precipitation. The information gathered allows meteorologists to forecast the commencement and severity of rainstorms, allowing individuals and administrations time to prepare.

"Satelittes gives us nearly 30-40 products (images) of which limited ones are shared with the public. Meanwhile, each Doppler radar covers an area of 500 km radius and gives a 360-degree picture of the precipitation. 40 such radars across India send snapshots every 10 minutes," explained the IMD director.

He elucidated that the IMD keeps receiving information on weather updates from all airports across India. Similarly, the ships have meteorological devices like barometers & anemometers and information recorded by these devices is received by scientists at the weather agency and used while forecasting the city's weather.

"We, at IMD, also release four balloons every day-once in the morning and one in the evening-to get recordings of the upper air weather. The balloons go up to 35-40 km high. Across India, 60 such balloons are released," Kamble explained.

Another scientist working at the IMD elaborating on it said that these balloons are attached to instruments that record weather patterns such as ridges, troughs, upper air disturbances, and upper lows.

Kamble, responding to a query said that these tools are used 24x7 through all seasons.

Weather models in forecasting

The scientists explained that after collecting the data, they use different weather models-which are based on complicated mathematical equations that represent the mechanics of the atmosphere, including temperature, humidity, wind speed, and pressure-to arrive at a forecast that aligns with prevalent weather systems.

The scientists explained that after collecting the data, they utilise various weather models. These models are grounded in complex mathematical equations that stimulate atmospheric mechanics, factoring in elements like temperature, humidity, wind speed, and pressure. By doing so, they can generate forecasts that accurately reflect the prevailing weather systems.

Certain well-known weather models, such as NOAA's Global Forecast System (GFS), provide long-range global forecasts up to 16 days in advance. The GFS is updated every six hours, ensuring that the predictions remain current and accurate.

The European Centre for Medium-Range Weather Forecasts (ECMWF) model is renowned for its accuracy in medium-range forecasting. It employs an ensemble approach, which enhances the reliability of its predictions. Meanwhile, the highly customisable Weather Research and Forecasting (WRF) model is widely used for regional forecasting and for predicting specific phenomena, such as hurricanes.

Other models, such as the UK Met Office's Unified Model (UM), provide detailed short-range forecasts, notably for the UK. Meanwhile, the High-Resolution Rapid Refresh (HRRR) model focuses on short-term, high-resolution forecasts, which are important for severe weather occurrences in the United States.

Long-term projections are backed by models such as the Climate Forecast System (CFS), which makes seasonal predictions. Ensemble Prediction Systems (EPS) and NAVDAS improve forecasting accuracy by taking into account a wide variety of possible weather events, resulting in reliable global and regional forecasts.

Challenges in forecasting Mumbai's weather

Although the technology of weather forecasting is advanced in India and at par with global standards, Kamble noted there are certain limitations in forecasting Mumbai's weather.

"Mumbai is a reclaimed city and there are several low-lying areas which flood easily. It becomes crucial for the IMD to provide impact-based forecast to different agencies like the disaster management agency to alert them," said Kamble and added, "however, giving accurate localised weather forecast is not possible."

The IMD official said that the microclimates in Mumbai cause considerable differences in weather over short distances, making it difficult to provide accurate citywide forecasts. For instance, one part of the city may have severe rainfall, while another may remain relatively dry.

"In such cases, it is very difficult to convince the people about the accuracy of the forecast. The public often questions the accuracy of our forecast if they don't experience rain outside their homes and it is one of the challenges before us," said Kamble.

While El Niño and La Niña events-which modify sea surface temperatures and wind patterns-cause Indian monsoon to be highly unpredictable, the issue has been exacerbated by climate change.

When asked about the impact of climate change and global warming which has escalated to global heating, Kamble said that extreme weather events have increased due to the phenomenon. He added that climate change and global heating have also led to an increase in the frequency of cyclones and caused changes in the monsoon patterns.

"Earlier, the coastal area saw a cyclone once in three years however off lately the frequency has increased. The region now sees a cyclone every year; additionally, the heatwave days have also gone up. This year Mumbai, witnessed at least four days of heatwave conditions wherein temperature went above 37 degrees Celcius. Every city has a set temperature range which is suitable for the residents. For coastal regions like Mumbai, temperatures soar above 37 degrees. C translates to heatwave condition," the IMD official explained.

"Mumbai's monsoon pattern has changed. For instance, this year, we have already received 2,200 mm of rainfall. Mumbai, on average, receives 2,300 mm of rainfall throughout the four months of monsoon. We already have received 550 mm of excess rainfall and most of the rainfall happened during nighttime. With monsoon patterns changing, long-term forecasting becomes a challenge," he noted.

Additionally, there is a data limitation, said the scientist highlighting that there are some areas where they don't have weather stations-automatic or physical.

The scientists also said that with the advent of social media, misinformation based on weather is circulated without verification. "There have been instances wherein people have used old products (satellite images) and shared misinformation regarding prevailing weather conditions which cause panic among the public," explained the senior official.

The path ahead

Despite the challenges, the IMD officials say their monsoon prediction is at least 85 per cent accurate.

The IMD is trying to expand our observational network with the installation of additional AWS (automatic weather stations). Expanding the observational network will give the department access to more data which will help in bettering the accuracy of the forecast, the official noted.

Meanwhile, the Met department, the officials said, issues Nowcast which upgrades their forecast every three hours. "Nowcast allows us to upgrade and downgrade alerts based on the prevalent weather systems," said Kamble.