Mumbai rains: What ‘Red’, ‘Orange’ alerts mean

A ‘Red’ warning denotes the likelihood of extremely heavy rainfall. Over 200 mm of rain is expected over the next 24 hours. The warning means that the authorities — in this case the Mumbai Police, Brihanmumbai Municipal Corporation (BMC), Mumbai Fire Brigade, National Disaster Response Force (NDRF), Railways, etc. — must take action.

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Colour-coded alerts

Alerts by the IMD are colour-coded from Green to Red. ‘Green’ stands for ‘No warning’: no action needs to be taken by the authorities, and the forecast is of light to moderate rain.

A ‘Yellow’ alert signifies “Watch”, and authorities are advised to “Be updated” on the situation.

Waterlogged Roads in Chembur East on Wednesday (Express Photo by Amit Chakravarty)

An ‘Orange’ warning stands for “Alert”, and authorities are expected to “Be prepared”. The forecast during an Orange warning is of heavy to very heavy rainfall.

A ‘Red’ alert stands for “Warning”, and asks authorities to “Take action”. The forecast is for extremely heavy rainfall. The IMD, however, clarifies that “Red colour warning does not mean ‘Red Alert’,” and that it only means “take action”.

Rainfall levels

According to the weather department, 15.6 mm to 64.4 mm rain is considered “moderate”, 64.5 mm to 115.5 mm is considered “heavy”, 115.6 mm to 204.4 mm “very heavy”, and more than 204.5 mm “extremely heavy” rain.

The Met Department had issued an Orange alert with forecast of heavy rainfall for Wednesday. However, at 2 pm, when the Santacruz weather observatory recorded 206.6 mm of rain, which falls under the “extremely heavy” category in six hours (8.30 am to 2.30 pm), the alert level was changed to Red.