SANDAG officials said the storm could create unsafe riding conditions during the morning and afternoon commute hours.
Riders who bike to work anyway should take extra safety precautions and be aware that no pit stops will be available, according to SANDAG, which helps coordinate the event.
The agency expects the rescheduled event to include originally planned activities, including pit stops where riders can pick up a free T-shirt and snacks, and receive encouragement. Bike riders are advised to visit www.511sd.com/iCommute for pit stop locations.
The National Weather Service forecasts a 90 percent chance of rain.
The expected wet weather has also forced the postponement of Friday's outdoor graduation ceremonies at Cal State San Marcos to Sunday, though Saturday's campus events are expected to take place as scheduled.