Bear Scotland has issued a warning to drivers that the A83 Tarbet to Campbeltown will be diverted at the Rest and Be Thankful due to the heavy rain forecast.
The decision comes as the Met Office issues a yellow weather warning until noon on Saturday, October 9.
Heavy rain could lead to potential landslides on the notorious stretch of road.
Traffic will instead follow a diversion onto the Old Military Road, a single-track road that is low to ground on the valley of Glen Croe.
The diversion will be in place from 3.30 pm on Thursday, October 7 until authorities deem the A83 safe enough to reopen.
An evaluation about reopening the road will take place on Friday morning.
Due to the Old Military Road being single-track, all traffic will be managed by a convoy operation throughout the afternoon and overnight to prevent potential accidents.
Argyll and Bute communities are forecast to expect intense and persistent rainfall with some predicting that nearly two inches of rain will fall in just 24 hours.
The A83 is currently under convoy operation until this afternoon before traffic is transferred to Old Military Road.
Eddie Ross, Bear Scotland’s north-west representative said: “We’re putting road-user safety first and diverting all traffic to use the Old Military Road from 3.30pm as a safety precaution due to tonight’s weather forecast of heavy rain showers.
“A band of heavy rain is expected to impact the area from this afternoon, with persistent rainfall expected throughout the night and into Friday morning.
“We have teams closely monitoring conditions in the area as well as the hillside above the A83, and we’ll assess the situation tomorrow morning with a view to re-opening the trunk road as quickly as possible if conditions permit and it is safe to do so.”