Complex sentence: Shortly after achieving peak intensity, Ophelia began to quickly weaken as it accelerated northeastward towards Ireland and Great Britain, becoming extratropical early on October 16, thus becoming the second storm of the 2017--18 UK and Ireland windstorm season.
Split into simpler sentences: Shortly after achieving peak intensity, Ophelia began to weaken as it accelerated northeastward towards Ireland and Great Britain. By October 16, the hurricane completed a transition into an extratropical cyclone, thus becoming the second storm of the 2017--18 UK and Ireland windstorm season.