Complex sentence: Impact from the storm in Mexico was most severe in Veracruz, where 13 people were killed by landslides--nine in Yecuatla, three in Tuxpan, and one in Atzalán.
Split into simpler sentences: Impact from the storm in Mexico was most severe in the state of Veracruz. There, 13 people were killed by landslides, nine in Yecuatla, three in Tuxpan, and one in Atzalán.