A person who feels overwhelmed tries to explain it in a handful of short, blunt lines. The speaker starts by listing how they see themselves: too emotional, quick to snap, in bad moods, with bad looks. These read like criticisms, maybe ones the speaker has heard from others or has started to say to themselves. Then comes a plain admission: "I cant handle much." There is simply too much going on.
The poem's turn comes in the last three lines. The speaker is crying "little by little," a slow, quiet release, but warns that it will soon become "a lions loudest roar." Quiet sadness is building toward something big and impossible to ignore. The title, "Thunderstorm," fits this idea, since a storm gathers before it breaks.
The mood is tense and fragile, like the heavy air just before rain. The short lines and missing apostrophes make it feel raw and unpolished, as if written in the middle of the feeling.