Jornal Do Brasilia - Third Low-Pressure System Expected Over Bay of Bengal as Tamil Nadu Monsoon Continues

Chennai: The Bay of Bengal is preparing for another significant weather disturbance as the region continues to recover from two successive severe cyclonic storms. Meteorologists are closely monitoring a low-pressure area expected to form over the southeast Bay of Bengal around November 13, an unusual development during the peak of the northeast monsoon season.

According to the India Meteorological Department (IMD), the low-pressure area is likely to intensify into a well-marked low within 24 hours. If conditions allow, it could develop into a depression or a cyclone, marking the third such system this year. This sequence follows the recent passage of Severe Cyclonic Storm Murasu and Very Severe Cyclonic Storm Arnab, a back-to-back occurrence that experts describe as rare.

Mahesh Palawat, vice president (meteorology) at Skymet Weather, noted that while two consecutive cyclones are uncommon, the current atmospheric setup warrants careful observation. "Two back-to-back cyclones are very rare," Palawat told The New Indian Express. "Now, another system is likely to form. It may intensify into a depression, but we have to wait. Different models are showing different tracks, with some indicating movement towards Andhra Pradesh and others towards Myanmar. The picture should become clearer over the next 48 hours."

Palawat stated that current models do not indicate an immediate threat to north Tamil Nadu, with several suggesting the system might recurve toward the northeast. However, he cautioned that warmer-than-normal sea surface temperatures could favor further intensification. He added that if this system strengthens into a cyclone, it would be the third in the North Indian Ocean this year, a region that typically experiences three to four cyclones annually across both monsoon seasons.

In response to recent weather patterns and safety concerns, the Fisheries and Fishermen Welfare Department has issued directives for all mechanized boats and motorized traditional fishing vessels operating from Chennai Fishing Harbour to return to shore by November 12. This measure follows the tragic loss of nine fishermen in recent incidents, underscoring the risks associated with the active monsoon phase.

Meanwhile, the Regional Meteorological Centre (RMC) has forecast heavy rain for isolated areas in Ramanathapuram, Thoothukudi, and Tirunelveli districts on Wednesday. These areas may experience thunderstorms, lightning, and gusty winds reaching 40-50 kmph. Moderate rainfall is expected across the Cauvery delta and southern districts, including Thanjavur, Tiruvarur, Mayiladuthurai, Nagapattinam, Pudukkottai, Sivaganga, Madurai, Virudhunagar, Theni, Tenkasi, and Kanyakumari. Light rain is anticipated in isolated parts of the remaining regions of Tamil Nadu and Puducherry.

Rain activity is expected to persist in parts of the delta and southern districts on November 12 before easing. The weather office forecasts mainly dry weather over most of Tamil Nadu on November 13, with rain returning to several coastal and northern districts, including Chennai, Tiruvallur, and Chengalpattu, on November 14. Heavy rain is also predicted for parts of the Cauvery delta on November 15, as well as in the Nilgiris and Coimbatore districts on November 16.

In a separate development aimed at improving monsoon forecasting accuracy, researchers from the Indian Institute of Technology Madras and Gauhati University have developed a new method to distinguish between short-lived local rainfall and the arrival of large-scale monsoon systems. The study, published in the Journal of Climate of the American Meteorological Society, utilizes a climate-network approach to track how rainfall at various locations across India gradually connects to form a large, interconnected system.

Traditionally, monsoon onset is identified based on the first rainfall at a specific location. However, this new method considers when local rainfall becomes part of the largest interconnected cluster of rainfall events nationwide. By analyzing 84 years of rainfall data, the researchers found that the average large-scale monsoon onset occurs around May 15 in Northeast India and June 9 over the Indian peninsula.

The study explains that small rainfall clusters develop over Northeast India during April, partly due to thunderstorms. As the season progresses, these clusters merge with rainfall activity over the Bay of Bengal to form a larger system. A similar process occurs over the peninsula, where rainfall activity over Kerala eventually connects with the larger monsoon system moving westwards from Northeast India. This research provides a more robust framework for understanding the spatial dynamics of the Indian monsoon.

M. Silva--JDB