"The high is still hanging on but it will slowly get worse. Coming in to tonight and tomorrow morning you'll see the real meat of the weather system.''
Temperatures are expected to remain about the same _ 15 to 16C.
Looking ahead, thick cloud are expected to hang over the region, which will bring patchy rain, Mr Corbett said.
It will slowly get worse as the week leads on and the rain will be "more persistent'' as another low creeps over the region.
"At the end of the week it's going to be really yucky,'' Mr Corbett said.
"The rain could turn quite heavy on Thursday and Friday. It's raincoat weather out there.''