The Portuguese Institute for Sea and Atmosphere has extended their weather warnings to 16 districts.
The forecaster is predicting heavy rain, with potential bouts of hail and stormy conditions.
Irish tourists should keep an eye on local forecasts and take necessary precautions in affected areas.
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"Periods of rain or showers, sometimes heavy and occasionally accompanied by thunderstorms. Drop in temperature, especially maximum and in the North and Central regions," forecasts IPMA.
Here is a breakdown of the rain warning levels across Portugal's main land, while the island of Madeira is in for stormy conditions:
Mainland Portugal
Aveiro - Yellow
Braga - Yellow
Bragança - Yellow
Castelo Branco - Yellow
Coimbra - Yellow
Guarda - Yellow
Porto - Yellow
Viana do Castelo - Yellow
Vila Real - Yellow
Viseu - Yellow

Madeira Archipelago
Madeira North Coast - Orange for rain, wind and coastal conditions
Madeira Mountain - Yellow
Madeira South Coast - Yellow for rain, wind and coastal conditions
Madeira Porto Santo - Yellow for rain, wind and coastal conditions
The Autonomous Region of Madeira will be under the yellow warning until midday on Thursday at least, with wind, rain and rough seas expected.
Due to the weather and sea conditions, Porto Santo Line maritime crossings have been rescheduled today.
Thursday's trips scheduled to depart from Funchal at 8 am and from Porto Santo at 8 pm “will be cancelled due to the bad weather conditions forecast for Porto Santo” reports The Portugal News.
This comes after large parts of Spain, Portugal and some parts of France were affected by a massive electricity cut yesterday.