They also should delay returning home by one or two hours if they want to avoid traffic jams, deputy city clerk Sanya Chenimit said yesterday.
The advice comes after many commuters complained on social media about being stuck in traffic on Wednesday. They say floods and traffic congestion added to delays.
"Staying one or two hours longer at your office may help alleviate traffic congestion," Mr Sanya said.
About 70-80% of Bangkok is expected to be affected by heavy downpours from this afternoon until tomorrow, according to weather forecasters.
Apart from low-lying areas, many parts of the city where roadworks are taking place such as on Phetkasem Road could be seriously affected because construction material is likely to block run-off reaching waterways and the drainage system, he said.
The Bangkok Metropolitan Administration aimed to drain floodwater from city roads within two hours, he said.
Traffic police chief Pol Maj Gen Jirasant Kaewsaeng-ek said many parts of Bangkok and outlying areas were affected by heavy rainfall early yesterday morning.
Traffic backed up on Sukhumvit, Poochao Samingphrai, and Theparak roads during the morning rush hour, he said.
Pol Maj Gen Jirasant also suggested people plan their commutes carefully when heavy rain is forecast, especially during peak hours.
He also recommended commuters check with the traffic police or listen to radio reports to find out if their routes are affected by floods or heavy traffic before they set off.
Prime Minister Prayuth Chan-ocha has put the military on standby to offer help during flooding if needed, said Winthai Suwaree, spokesman of the National Council for Peace and Order.
He said more heavy rainfall is expected around the country, which could result in flooding in many areas.