Potential impacts include coastal flooding, damage to temporary structures, difficult travelling conditions and wave over-topping, which are most likely in western parts of both counties.
It will come into effect at 7pm on Wednesday evening and remain in place until the early hours of Thursday to lift at 2am.
Hurricane Ernesto, which ripped through the Caribbean over the weekend at speeds of 136kph, left many without power in Bermuda and Puerto Rico.
The remnants of the storm will lead to wet and windy weather on Wednesday through to Thursday as it passes over Ireland and the UK.
It is currently classified as a “post-tropical storm”, with a Status Yellow gale warning already in place from Rossan Point to Bloody Foreland to Fair Head until 9pm tonight.
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Winds are expected to reach gale force 8, with Met Éireann issuing similar warnings over the coming days.
These warnings are in place on Wednesday from 11am until 8pm, with the second in place from 8pm on Wednesday until 10am on Thursday.
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It comes as smoke from wildfires burning in western Canada has travelled across the north Atlantic to reach Europe, potentially contributing to “hazy” sunsets and reduced air quality.
An analysis by the Copernicus Atmosphere Monitoring Service has shown “significant smoke” travelled between August 10 and 19, leading to high Aerosol Optical Depth (AOD) values reaching Ireland, the UK and parts of the continent.
AOD is the measure of particulate matter and aerosols such as desert dust or smoke particles that are distributed within a column of air from the surface of the Earth to the top of the atmosphere.
The large-scale fires have been ongoing for several weeks following a period of heatwave conditions, with the intensity and emissions of wildfires increasing sharply since the beginning of August.
Smoke from Canadian wildfires last June led to delays at major US airports as it impacted visibility, air quality and contributed to high levels of pollution on the east coast, resulting in the issuing of health advisories due to the short-term effects.
Viral photographs showed New York landmarks covered in an orange haze and almost obscured by smoke as the sky took on an eerie hue.