Remnant of Ditwah pounds Chennai, neighbouring dists

RMC changes rain alert from orange to red within 4 hours . Holiday for schools, colleges in Chennai and 3 other districts

- SV KRISHNA CHAITANYA @ Chennai

A stubborn, slow-moving deep depression - a remnant of Cyclone Ditwah - that defied forecasts for two days slammed Chennai and its neighbourhood with intense rain on Monday, sharply reversing expectations after appearing to weaken over the weekend.

Meteorologists described the weather system as a "highly complex" system that exposed the limitations of numerical weather prediction in the Bay of Bengal.

From issuing an orange alert at noon on Monday to upgrading it to a red alert barely four hours later, the Regional Meteorological Centre (RMC), Chennai, was forced to respond to a rapidly evolving atmosphere. This system has been challenging and erratic from the beginning, as there were multiple circulations in the open oceans, interaction with the Sri Lanka landmass, fluctuating wind shear and at least two false starts in convection buildup.

According to the met office, the deep depression is expected to weaken gradually into a depression. However, as it will continue to hug the coast and remain within 30 km of Chennai, moisture convergence is likely to persist.