More than one accepted pronunciation. English and Americans seem to go for "howl" whereas my Welsh family have always said it the same as Howell, with two syllables. I have also heard "huel" but only once. [noted -ed]
Hywel Dda (Howell the Good), who died in AD 950, is remembered above all for his codification of Welsh Law. The laws provide an important insight into life in Medieval Wales.