How do you know if prevailing westerlies affect the climate? Explain which part of Europe is most affected?

Western coast of Europe is the most affected. Back in the day they used to called westerlies the "anti-trade" winds because travelling cross atlantic took longer. They affect the climate because they carry remnants of tropical storms formed in the Caribbean and Eastern USA across the pond, which eventually reaches Spain, France and the UK (and to a certain degree the Netherlands). They also carry warm winds and waters.