The Met Office has warned of travel disruption as gusts of up to 60mph are expected.
A spokesperson for Ireland's national forecaster said: "At the moment we are experience severe weather, with severe winds and heavy rain".
"A yellow wind warning is in place on Wednesday until 3am on Thursday".
"I have to stress there is a lot of uncertainty to this next system overnight and the worst of the winds could be reserved for more northern areas of the country".
Severe rainfall will affect other parts of the United Kingdom, with the storm expected to bring between 60mm and 80mm of rain.
Western parts of Britain, including Northern Ireland, south-west England, Scotland and Wales, are expected to bear the brunt of Diana's force on Wednesday.
"We are working closely with the Met Office and other agencies to allow us to make informed decisions, to ensure we have staff on the ground where needed", the company said.
"It's followed by another one on Thursday and if anything this one could have even stronger winds, particularly across parts of the west, so we do have warnings in force".
A status Orange alert has been issued for six counties in the West, South and Southeast.
While it will be mild with temperatures hitting 15 degrees Met Éireann expects the unsettled weather to continue into the weekend. But drier, less windy weather, with bright spells and scattered showers over Munster will extend countrywide this afternoon.
"Rain and the strongest winds will gradually retreat to the North East".
The Met Office statement on the warnings added: "Rain will become persistent and heavy at times across parts of north-eastern Scotland on Wednesday afternoon and evening". Yet more rain and strong winds expected next Saturday night and on Sunday.