Two prevailing weather systems close to the Tamil Nadu region are expected to influence heavy rainfall across many districts till October 13. The Regional Meteorological Centre (RMC) has issued an orange warning, indicating the possibility of isolated very heavy rainfall over Nilgiris district on Saturday.

While the northeast monsoon is likely to arrive around October 16-18, the RMC has noted that districts like Tirunelveli and Tenkasi in extreme southern T.N. may experience below-normal rainfall during the upcoming season. In contrast, northern districts may receive above-normal rainfall, according to the long-range forecast.

The State may continue to experience wet weather for the next six days. On Saturday, heavy rainfall may cover 10 districts, including Tiruppur, Coimbatore, Sivaganga, and Salem.

Two upper air cyclonic circulations- one over north coastal T.N. and another over north coastal Andhra Pradesh and neighbourhood- would bring rainfall to several parts of the State.

Officials of the RMC noted that simultaneous withdrawal of southwest monsoon and onset of easterly/ northeasterly winds that herald the NE monsoon are likely between October 16 and 18.

B. Amudha, Head (Additional in-charge), RMC said in the past 15 years, Tamil Nadu has recorded above normal NE monsoon in most years except for two. This year, NE monsoon over T.N., Puducherry, and Karaikal is expected to be normal to above-normal, with a seasonal rainfall of 44 cm-50 cm.

Rainfall has been deficient in some districts, including Chengalpattu, Pudukottai, and Kanniyakumari, since the start of October.

On the forecast of cloudbursts, Ms. Amudha noted that rainfall of about 10 cm received within an hour over a particular area qualifies as cloudburst. While the exact quantum of rainfall particularly during intense thunderstorm activity cannot always be predicted with 100% accuracy, the rainfall intensity was reasonably forecast during recent events in Chennai.

The RMC has forecast thunderstorms, which is typical during the transition phase between monsoons, to occur in some areas of Chennai on Saturday.