The storm strengthened from an area of disturbed weather that passed over the central Yucatan Peninsula two days before it struck Veracruz state.
Fernand attained tropical storm force for only 15 hours before breaking apart over the rough interior of Mexico.
But it produced winds of up to 40 mph and torrential rains that triggered slides that came down on most of the 13 victims' homes.
Veracruz Governor Javier Duarte said Fernand was “atypical” because of how quickly it formed into a tropical storm over the Gulf of Mexico late Sunday before making landfall.
Fernand is the fifth named storm of this year's Atlantic hurrican season, which runs from June 1 to November 30.
The season has so far been unusually quiet with no full-fledged hurricanes yet to develop and only a handful of relatively weak tropical storms.
Tropical Storm Fernand Track