The steam can be seen when the car is parked with the engine still running. The steam cant be seen once the car is moving tho. The dash coolant temperature gauge remains normal at around 90 - 95 degree celsius.

 

An update of the issue of my 996tt, it didn't lose any coolant according the level of coolant bottle in the engine bay and no steam is coming out from the from drive side radiator as well. I only noticed the steam after rain or a car wash. Furthermore, the coolant temperature wasn't 90-95C. Instead it was only 80-82c or so.

To sum up,
1 no coolant loss
2 no steam in the dry (even after some driving n idling)
3 coolant temp 80-82C
4 that radiator was replaced at deal in 2009

I hope it is just some curd or turd or tissue paper sticking onto the radiator. I plan to remove e bumper myself but I am worried with my limited skill, I might damage the paint on the bumper in the process.