The alert came into effect at midday on Sunday and is due to remain active until 9pm, with forecasters warning of periods of heavy rain and showers across the country.
Some of the heavier downpours could be accompanied by thunderstorms, with lightning and hail also possible in places.
The unsettled conditions could lead to a number of weather-related impacts, including small localised flooding and reduced visibility. People travelling during the warning period are being advised to take extra care, particularly where heavy showers develop.
There is also the potential for lightning-related damage, while outdoor events could be disrupted by the difficult conditions.
Despite the warning, there will be some brighter intervals during the day, with occasional sunny spells expected between showers.
Temperatures are forecast to reach between 16 and 21 degrees, with winds generally light to moderate and coming from southerly or variable directions. Gusty conditions may develop during the heavier showers.
The unsettled weather will continue into Sunday night, although showers are expected to become less frequent as the evening progresses.
Clearer spells will develop overnight, but it will remain breezy, with moderate to fresh west to northwest winds. Winds will be particularly strong along Atlantic coastal areas.
Overnight temperatures are expected to fall to between 10 and 14 degrees.
Those attending outdoor events or travelling across the country this afternoon are advised to keep an eye on the latest forecasts and allow additional time for journeys where necessary.
