Hi David, apologies for the delay in replying. The lines measure air thickness in our atmosphere – basically north of the red line is thick/humid/tropical and south of the blue line it’s thinner/dry/colder air. The area in the middle is the more temperate climate we live in most of the time. It doesn’t mean it’s stormy between them necessarily – but usually there will be a driving force behind them, like a storm in the Southern Ocean or the monsoon trough shifting over the tropics – or a tropical cyclone pulling that red line down. The lines being closer together don’t cause a problem – but there will likely be a culprit somewhere in the weather maps (or just off the screen).
Cheers
Phil D