Gusty winds may also blow at 40km per hour speed
The Pakistan Meteorological Department has forecast heavy monsoon rains in Karachi from Monday till Wednesday.
The city is expected to receive more than normal rains this time, according to the Met Office.
The rain would continue to intermittently lash the city until Wednesday morning, Chief Meteorologist Sardar Sarfaraz said.
Likely to be coupled with a thunderstorm, it may trigger flash flooding in the megapolis. The PMD has forecast up to 40mm rain in Karachi over the next three days.
Gusty winds are also expected to blow in the city at a speed of 40km per hour, according to the Met Office.
It has asked Karachiites to take precautionary measures and not to stand underneath trees and banners.
A few areas of the city received drizzle Sunday evening too. It brought the temperature down by four degrees to 30°C.