Complex sentence: The weather system ultimately accounted for at least $18.5 million (2010 USD) worth of damage throughout the Caribbean, where it was widely regarded to be one of the wettest storms in recent local history.
Split into simpler sentences: The weather system ultimately accounted for substantial losses throughout the Caribbean, preliminarily pinned at over $20 million (2010 USD). It was widely regarded to be one of the wettest storms in recent local history.