Rain or shine, or both? Nobody knows

CHENNAI: For over a decade, technology for weather forecast accuracy has been improved in the meteorological department, where the five-day forecast has been predicted accurately until recently.

However, it failed to predict heavy rain on Sunday when several parts of the city and suburbs experienced sudden downpours and recorded 7-10 cm of rainfall within a few hours.

Pointing out that climate change plays a crucial role that has a significant impact on weather conditions, the Regional Meteorological Centre (RMC), Chennai, stated that the model cannot predict the exact weather pattern.

Due to a change in trough wind over the sea, Chennai, Tiruvallur and Kancheepuram districts witnessed an increase in rainfall activity. The weather department’s forecast was light to moderate rain over a few districts, with a possibility of intense spells in other areas.

“We have predicted moderate rain for Chennai and neighbouring districts, but the model won’t be accurate to predict rainfall pattern. When there is a system formed over the sea, we would forecast the areas where rains are likely to occur. Heavy rain was expected over the ocean due to the trough wind. Since the trough shifted towards the left, the rainfall activity increased in Chennai, Tiruvallur, and Kancheepuram districts on Sunday evening. Sometimes the system might be prominent or weak,” explained P Senthamarai Kannan, director of the area cyclone centre, RMC.

The model scale length would be 12 sq km which would predict rainfall activity and not an accurate amount of rainfall record. The official mentioned that if the model predicted there would be heavy rainfall in the city, the warning would have been issued.

If the city receives 6 cm of rainfall, it’s considered to be moderate rain, and 7 cm and above is heavy spells.

“The meteorological department uses models to predict prevailing atmospheric conditions over the sea. There is no device for accurate rainfall prediction,” added Senthamarai.

There are four radars to cover weather data in the State, which function round the clock to predict weather conditions. The weather models have increased, and they provide accurate forecasts in the last few years.

In the last decade, there has been advancement in the equipment used to predict weather conditions, where hourly and monthly forecasts are provided. In addition, the department will state the impact caused by the depression or cyclones in TN.

There are 3D forecasts available for the public to understand the system over the sea better. On the other hand, with changes in weather conditions often in the city, the city corporation tracks rainfall patterns through several devices, weather websites, and independent bloggers.

J Radhakrishnan, commissioner, Greater Chennai Corporation said, “If the city receives 9-10 cm of rainfall, it’s manageable since we get updates every three hours. Plus, we’re also aware that 100% accurate prediction of rainfall activity is not possible.”

On Monday, a few areas including Kathipara and Ayanavaram witnessed water stagnation due to a non-functional motor pump, and storm water drain constructions in the respective areas. It was drained out the next morning without causing interruption to the traffic flow.

Radhakrishnan added, “Similarly, on June 18, Chennai and its suburbs witnessed widespread rainfall. The weather station recorded the highest rainfall with 9 cm and 13 cm respectively, where several areas were waterlogged, but it was pumped out within few hours. The south and central Chennai areas received intense spells in a short span. We have sufficient manpower and equipment to handle to situation.”

The Integrated Command Control Centre (ICCC) at Ripon Building monitors the rainfall activity at the ward level. “The IMD is the authorised department to forecast weather conditions, since they have 2-3 devices. However, we’ve installed 30 devices in the zone and unit office in the city. In that case, the corporation officials will be given a forecast report 72 hours before. So, they can be proactively aware of the situation,” explained G Rajeshwari, system analyst who heads the ICCC.

The civic body issues weather forecasts every hour through IoG devices to the officials during the monsoon season. In addition, the centre shares the real-time rainfall data and forecast with other departments too.