Monday, August 1, 2011

Emily Taking Shape in the Atlantic?

It is a long ways out (meteorologically speaking) but a great tropical system is about to take shape in the tropical Atlantic. Long range models are showing a well-developed center of low pressure forming and making landfall on the southern tip of the Florida panhandle. This storm, should it become a tropical depression/storm/hurricane will be the 5th such storm this season. Storms are named once they reach a Tropical Depression status with a distinctive closed circulation. Should this disturbance reach that stage and from all indications it will, Emily will be its name!

What kind of shot does Emily have of actually making a U.S. landfall? Let's take a look.

Here is a look at the precipitation forecast from today that is valid for this Thursday. Notice the high precipitation forecast down in the Caribbean near the Dominican Republic. By this point, Emily should be at the least a Tropical Storm. The wild card to development is whether or not the storm makes landfall on Hispaniola. If it does, Emily could be torn apart by the friction of the land. But hurricanes don't like to be on land, so sometimes a storm will shift its path to avoid land and actually just skirts right around it. If that happens, the storm will have more chances to intensify in the warm waters.
This forecast is valid for Saturday morning. Clearly the model is showing Emily making landfall in southern Florida. But is there a shot that Emily misses the Unites States entirely and just swings out to the open Atlantic? Of course, but the "steering mechanism" reinforces a U.S. landfall.
The 500mb map shows us "roughly" where systems will go. Two things to note in this map, valid for Friday. One: The high pressure over the a bulk of the South. Circulation around the high pressure is in a clockwise patter. You can visualize air moving around the central area of high pressure. Winds will "pull" Emily onshore, giving us the landfall the models have shown above.
The second point is the ridge of high pressure that is building up in the New England area. This is critical to storm intensification. Higher pressures to the north means lower pressures to the south and that helps deepen the low that enters the Caribbean/Gulf of Mexico region. These two points back up the prediction of Emily making an intense landfall.

But just a few days later, things appear to change. This map is valid for next Monday, a week out. The high pressure region over the South has disappeared, due to Emily interacting at close range with the high pressure area. Along with the weakening high pressure, a trough just off the N.E. Atlantic coast has developed. Notice the wind barbs are showing a westerly flow. Emily will "feel" this trough and hitch a ride with it. Eventually, Emily will be pulled out to the Atlantic.
The precipitation map valid for next Monday does show Emily moving back over Atlantic waters and a rapid weakening of the storm will continue. The evolution of Emily will depend on several things, most of which I have mentioned. Land and intensification play roles, but so does storm speed (fast or slow moving) and water temperature. Nearly 7 days out however, Emily may become the first named storm in nearly 2 years to make landfall in the United States!

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