While there are currently no warnings in place, the forecaster has predicted intense weather which will bring with it risks of travel disruption and flooding.
The warning covers Central, Tayside, Fife, Strathclyde, Highlands and Eilean Siar, and predicts widespread heavy rain falling from Wednesday evening through much of Thursday, Friday and into Saturday.
It comes into force at midnight on Thursday and will remain in place until 12pm on Saturday, October 9.
When the initial warning was announced it included Perthshire, which has now been removed. However, the warning now extends slightly further north to include Skye and Lochaber.
Accumulations of 40-70mm will build up across the country with some areas in Argyll and West Highland seeing 100-150mm.
The Met Office has said there is currently some uncertainty over which areas will see the heaviest spells but the rain should gradually ease through Saturday.
Warnings of floods and damage to buildings, as well dangerous driving conditions and delays have been issued by the forecaster.