Interesting bit of history here. The deadliest F1 (and deadliest weak) tornado in history, the 1978 Whippoorwill tornado. 16 fatalities were recorded when the boat it hit was capsized on Lake Pomona. Despite being very narrow and weak, eyewitnesses saw 3 funnels rotating within it, indicating it had a multivortex structure. This event is an important reminder that all tornadoes, even weak ones are deadly and should be taken seriously.
When we think of deadly tornadoes, it's usually the big violent ones that come to mind. Their weaker counterparts can also inflict significant damage.