by David Murphy
Yes. They're called tropical storms and hurricanes. These are always shown on weather maps without fronts attached, because they do not form the same way as traditional low pressure systems. Rather than forming along the boundary between two different air masses, tropical lows form in a uniformly warm and moist environment. The trigger for formation is the vast amount of evaporation from warm sea water, causing an enormous amount of rising air and moisture.
The technical name for this type of low, by the way, is a tropical cyclone. Traditional lows (the kind with cold and warm fronts attached) are called extratropical cyclones. The word cyclone refers to the direction in which the winds are rotating and not a tornado, as is sometimes believed.