Complex sentence: Hurricane Matthew is currently a powerful tropical cyclone over the Caribbean Sea and the first major hurricane to form in that region since Hurricane Sandy in 2012 and the first category 4 hurricane occuring in September since Hurricane Katia in 2011.
Split into simpler sentences: Hurricane Matthew is currently a powerful tropical cyclone over the Caribbean Sea. It is the first major hurricane to form in that region since Hurricane Sandy in 2012 and the first Category 4 Atlantic hurricane occurring in September since Hurricane Katia in 2011.