This is the 14230th most frequent German word.
heftig
Intense, severe, or vehement.
The word 'heftig' is used here to describe the intensity of the storm, signifying 'severe' or 'intense'.
Das Unwetter war gestern Nacht wirklich heftig.
The storm last night was really severe.
In this context, 'heftig' describes the nature of the reaction, meaning 'intensely' or 'strongly'.
Er reagierte heftig auf die Kritik und wurde laut.
He reacted intensely to the criticism and raised his voice.
Here, 'heftig' conveys the emotional intensity of the discussion, interpreted as 'heated'.