You probably know that the "L's" that meteorologists use on weather maps stand for low pressure, or as some folks tell me, "Lousy weather," because lows typically bring clouds and precipitation. Lows are the storms.

Hurricanes are low-pressure systems too, so they share similarities with the more common lows that bring us precipitation every few days. For example, winds around all low-pressure systems in the Northern Hemisphere blow in a counterclockwise direction, with the air tending to converge toward the center of the low. However, one of the big differences between the run-of-the-mill low-pressure system and a hurricane is in their vertical structure.

In a non-tropical low-pressure system, the air in the column above the low is relatively cold compared to surrounding air. For this reason, meteorologists call such lows "cold-core" systems. Hurricanes, on the other hand, are "warm-core" systems. The column of air above the center of a hurricane is relatively mild compared to surrounding air. This abundance of warm, relatively light air is what keeps the pressure so low in the middle, or eye of the hurricane. In fact, if you judge a storm's intensity by how low its pressure is, then hurricanes are far and away the greatest storms on earth.