The India Meteorological Department (IMD) has forecast a prolonged spell of heavy to very heavy rainfall across Tamil Nadu, Puducherry and Karaikal until October 26, 2026. The weather department has linked the expected rainfall to a developing weather system over the southwest Bay of Bengal and the adjoining Tamil Nadu coastline. According to the forecast issued on October 21, a low-pressure area is likely to develop over the southwest Bay of Bengal and nearby coastal regions within the next 24 hours. The system could influence atmospheric conditions across southern India, bringing further rainfall to several areas over the coming days. The latest IMD weather alert covers multiple states and territories, although the expected timing and distribution of rainfall differ by location. Tamil Nadu, Puducherry and Karaikal are expected to experience a longer period of potentially intense rainfall, while other parts of southern India are also likely to receive heavy showers on specific dates. The developing system over the Bay of Bengal is therefore an important factor in the regional weather outlook. Residents, commuters and people planning outdoor activities should monitor official forecasts as the situation develops.

Tamil Nadu and Puducherry Face an Extended Rainfall Spell

Tamil Nadu and the Union Territory of Puducherry are among the main areas highlighted in the latest heavy rainfall warning. The IMD expects heavy to very heavy rain to continue in these areas through October 26. Karaikal, which forms part of the Puducherry Union Territory, is also included in the forecast. The expected rainfall is associated with a cyclonic circulation persisting over the southwest Bay of Bengal and the adjoining Tamil Nadu coast. A low-pressure area may form under the influence of this circulation, potentially supporting further rain-producing weather activity. For residents of Chennai and other parts of Tamil Nadu, the developing system makes regular weather updates particularly important. However, the available forecast does not establish that every district or city will receive the same amount of rainfall. Local conditions may vary depending on the movement and development of the weather system. People travelling between cities, using roads in areas prone to waterlogging or planning outdoor events should check location-specific forecasts before making decisions.

Why Is Heavy Rain Expected Over South India?

The developing weather system over the Bay of Bengal is central to the current rainfall forecast. According to the IMD's update, an upper-air cyclonic circulation was persisting over the southwest Bay of Bengal and the adjoining Tamil Nadu coast. The circulation extended to approximately 5.8 kilometres above mean sea level. Under its influence, a low-pressure area was expected to form over the same general region within the following 24 hours. A trough associated with the circulation extended towards north coastal Andhra Pradesh at approximately 3.1 kilometres above mean sea level. These atmospheric features are being monitored because they can influence the development and movement of rain-bearing systems. The weather department also reported another upper-air cyclonic circulation over the Gulf of Thailand and neighbouring areas of Thailand and Myanmar. This system extended to approximately 4.5 kilometres above mean sea level in the morning observations. These are forecast developments rather than confirmation that every predicted stage has already occurred. The department's subsequent updates will provide a clearer picture of the systems' progress.

Kerala and Mahe May Receive Heavy Rain Until October 26

Kerala and Mahe are also expected to experience isolated heavy rainfall during the October 20 to October 26 period. The forecast indicates that rainfall could occur at scattered locations rather than affecting every part of these regions uniformly. The intensity and timing of showers may differ according to local weather conditions. Residents in Kerala should follow regional weather bulletins, especially when planning road journeys, outdoor work or activities in areas that are vulnerable to heavy rainfall. Mahe, a coastal district of the Puducherry Union Territory located within Kerala, is also covered by the IMD's forecast. Its inclusion highlights the wider geographical reach of the weather system affecting southern India. The department has not provided a uniform rainfall total for every location in the supplied forecast. Therefore, the expected conditions should be interpreted as a regional warning rather than a prediction that every area will experience equally intense rain.

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Lakshadweep Rain Forecast From October 22 to 26

Lakshadweep is expected to experience isolated heavy rainfall between October 22 and October 26, according to the IMD. The island territory's forecast period begins a little later than the period specified for Tamil Nadu, Puducherry, Kerala and Mahe. As with the other regions, the term isolated heavy rainfall indicates that heavy showers may occur in particular locations rather than continuously across the entire territory. Weather conditions are particularly important for island communities because rainfall and changing atmospheric conditions can affect outdoor activities and travel planning. Residents should check official updates before making arrangements that depend on local weather. The forecast does not establish specific disruptions to ferry services, flights or other transport operations. Any travel-related decisions should therefore be based on updated information from the relevant authorities and service providers.

South Interior Karnataka May Experience Heavy Showers

The IMD has forecast isolated heavy rainfall over South Interior Karnataka from October 21 to October 24. This forecast places parts of the state within the period of unsettled weather affecting southern India. However, the warning is specific to South Interior Karnataka, and it should not automatically be interpreted as applying equally to every part of Karnataka. The timing of rainfall may vary across the region, depending on local conditions and the development of the broader weather system. People planning journeys or outdoor activities in the affected areas should follow the latest regional forecast and any advisories issued by local authorities. The IMD's updates over the next few days will be important in determining whether the rainfall outlook changes as the Bay of Bengal systems develop and move.

Andhra Pradesh Rain Alert: Forecast Extends Until October 23

Parts of Andhra Pradesh are also expected to receive heavy rainfall during the current weather spell. According to the supplied IMD report, heavy rain is likely in Coastal Andhra Pradesh, Yanam and Rayalaseema between October 20 and October 23. The forecast also mentions the possibility of thunderstorms and strong winds in connection with the unsettled weather. The expected conditions mean that people in these regions should pay attention to local weather bulletins, particularly when planning road travel or outdoor activities. Rainfall may vary considerably from one location to another. The forecast does not establish that all districts in Andhra Pradesh will receive heavy rain or experience the same weather conditions. Residents should also distinguish between a regional rainfall forecast and a location-specific warning. The latter may contain more detailed information about expected timing, intensity and any recommended precautions.

What the Bay of Bengal Weather Systems Could Mean for the Region

The IMD is monitoring two weather features described in its October 21 update: a circulation over the southwest Bay of Bengal and adjoining Tamil Nadu coast, and another circulation over the Gulf of Thailand and neighbouring parts of Southeast Asia. The first circulation is expected to support the formation of a low-pressure area near the Tamil Nadu coast. The second is forecast to move towards the north Andaman Sea before potentially contributing to the development of another low-pressure area over the Bay of Bengal around October 23. The systems are at different stages of development, and their subsequent movement will determine how weather conditions evolve across the region. Low-pressure systems can influence rainfall by supporting rising air and the development of rain-bearing clouds. However, the amount of rain received at a particular location depends on several factors, including the system's strength, movement and interaction with surrounding atmospheric conditions. The forecast therefore needs to be followed over time rather than treated as a fixed prediction for every location.