The India Meteorological Department (IMD) on Thursday predicted heavy to very heavy rainfall at isolated places in Mumbai and adjoining coastal districts, and issued an orange alert for the next two days.

An orange alert implies that authorities should be prepared to handle any situation arising out of severe weather condition.

Ratnagiri district, which bore the brunt of cyclonic storm Nisarga last month, is likely to receive extremely heavy rainfall at isolated places on Friday, while Raigad will receive similar downpour on Saturday, senior director of IMD Mumbai, Shubhangi Bhute, said.

Heavy to very heavy rains are likely to lash isolated places in Mumbai, she said.

As per the IMD's calculations, a rainfall between 64.5 mm and 115.5 mm in 24 hours is considered as heavy rainfall, while a downpour between 115.5 and 204.5 mm is very heavy rainfall.

Rainfall above 204.5 mm in 24 hours is categorised as extremely heavy rainfall.

"An orange alert has been issued for Friday and Saturday for areas that are likely to witness heavy showers and citizens and authorities in these places will have to stay vigilant," another IMD official said.