The Atlantic Main Development Region (often referred to as the MDR) is often cited in hurricane seasonal outlooks as a critical area to watch.This area, bounded in a box from 10-20N and 20-85W, is called the Main Development Region because, generally speaking, that’s where most westward moving tropical waves develop into tropical cyclones during a typical Atlantic hurricane season.
In terms of hurricane activity from one year to the next, the Atlantic is the most highly variable hurricane basin in the world. Some seasons, like 2007, have very little development or activity in this region, instead seeing development from “non-tropical” origins, such as at the base of stationary mid-latitude fronts.
Seasons with significant MRD activity/development, such as 2003, 2004 and 2008, are indicative of favorable conditions in the MDR for tropical systems (which of course makes sense). Generally, favorable conditions in the MDR during hurricane season lead to very active hurricane seasons (overall).
Therefore, seasonal hurricane forecasts often try to predict what conditions will be like in this key region during the peak months of the Atlantic season (August, September and October).
Here are three key MDR factors to watch both before and during the upcoming hurricane season:
1. Sea Surface Temperatures. Warm water is the fuel that drives hurricane intensity. The more heat contained within the water, the more energy is available for a particular storm. When water temperatures are warmer than normal, more/stronger hurricanes tend to develop than if water temperatures are below normal.
2. Surface Pressures. When surface pressures are high in the MDR, less tropical systems develop. Why? The theory is that higher surface pressures tend to suppress upward motion in the tropics, hence creating an inhibiting factor for tropical development. Therefore, lower than normal pressures tend to lead to more development…higher than normal = less development.
3. Low/mid level moisture. Hurricanes prefer wet, moist tropical environments for development. When dry air gets tangled up with a tropical cyclone, it can almost immediately put a lid on thunderstorm development, much like throwing cold water into a boiling pot can stop the water from bubbling. Hence, we can observe more activity in the MDR if low and mid level moisture values are relatively higher than normal there.
Over the next week, I will be looking at each of these three factors closely to determine what they can tell us about the upcoming 2013 hurricane season.