The past few days were bright and sunny but rain is lurking in the corner.

A depression over the Bay of Bengal advancing towards land is expected to bring rain to coastal Bengal and pockets of North and South 24-Parganas on Saturday, a Met forecast on Tuesday said.

“A depression has formed over east-central and adjoining southeast Bay of Bengal and North Andaman Sea,” according to the forecast.

“On Tuesday morning, it was positioned about 1,000km from the Sagar islands. It is very likely to intensify into a deep depression during next 12 hours and into a cyclonic storm over the subsequent 24 hours.”

The amount of rain the system is likely to bring to the city depends on the route the system takes, a Met official said.

The system is likely to move west-northwest initially and then north-northwest, towards Bengal and the adjoining north Odisha and Bangladesh coasts.

“If it moves towards the Bengal coast, then coastal districts and some pockets of South and North 24-Parganas are expected to get heavy rain (more than 60mm in 24 hours) on Saturday,” the official said. “The showers could be accompanied with wind clocking 40-50kmph, which could start blowing on Friday.”

But there is a possibility of the system skipping the Bengal coast and moving towards Bangladesh or Odisha. In that case, Calcutta and other parts of coastal Bengal will be spared heavy rain. “The picture will be clear in the next couple of days,” the official said.

In either case, the Celsius is set to rise in the coming days and so is the humidity level.

The maximum temperature had been under 32 degrees Celsius for seven days till Monday, when it was 32.1.

The minimum relative humidity — a measure of the moisture content in the air during the warmest part of the day — has been hovering in the 50 per cent range. On Sunday, it plunged to 49 per cent.

But things are going to change in the coming days. “The daytime temperature is set to go up a notch or two. The humidity in the air will go up because of moisture incursion from the Bay,” a weather scientist said.

The Southwest monsoon had officially retreated from Calcutta on October 14. But a low-pressure area over Westcentral and adjoining Southwest Bay of Bengal brought sharp spells of rain to the city in the run-up to Diwali.