Tropical Update August 10th, 2008

I made one major mistake yesterday in my blog post, and that was that the GFS was a little fast in forecasting a system to develop in the mid-Atlantic in 3-5 days. After looking at another day's worth of model runs, consistency from other models (including the UKmet, European, and CMC) and it looks much more likely that a system will develop in the mid-Atlantic in the next 3-5 days. I don't think the question is will a storm develop, but rather how strong it will be and where it will go.

There are three possible locations in which a tropical system could develop in the next week. Two disturbed areas are currently located in the central Atlantic, highlighted on the Tropical Weather Outlook below. Both systems are categorized in the moderate risk of development category by the National Hurricane Center with text saying "some development is possible during the next couple of days." In other words, the NHC is interested in these locations for possible development.

In the satellite picture below I have circled the two disturbed locations. Both seem to have some cyclonic turning and are located in regions of low shear, high sea surface temperatures, and have some decent convection. The system to the west currently looks the most robust, but the models are having trouble developing that system (except for the CMC) and instead develop the eastern system. If I had to pick one to develop in the next two days, I would pick the system to the west with its strong convection and greater separation from the ITCZ. The main inhibiting factor is the very dry air to the west of the system which could cut off its development quickly. The eastern system still has to break away from the ITCZ to get itself together. However, I do expect it to develop in 3-5 days just as all of the models are predicting in a favorable environment.

The models vary strongly on the strength and track of the system. The GFS and CMC develop the eastern system quickly, in 2-4 days, and strengthen it to a hurricane, maybe even a major, before it reaches the islands. If this is true, the storm will be strong enough to feel the trough along the eastern seaboard and pull north as a developing low pressure system emerges off of the Carolinas. However, the European does not develop the system quite as quickly, and keeps the system weak. This allows it to slide under the trough and into the Gulf of Mexico.

Further systems are forecasted to develop behind these two current waves, including one wave that is moving off of the African coast as we speak. All three models (GFS, CMC, and European) develop this wave and move it across the Atlantic towards land. Obviously we are entering a busy period in the tropics! Below are the GFS and European model solutions for the eastern system shown in the satellite picture above. This system is numbered #1, followed by the African coast system as #2, and then further into the future systems as higher numbers. The model output is from hour number 240, or 10 days out.

GFS:

European:

So what does this tell us? We need to keep watching these systems as all of the models forecast them to impact land at some point. The GFS solution seems like the worst case scenario with a strong system moving up the eastern seaboard, possibly impacting New York. However, at 10 days out this is very difficult to forecast. Remembering back to the discussion of Asia yesterday, our only hope is that the eastern trough doesn't break down as fast as the models are predicting and the system numbered #1 is brought out to sea. However, considering the models keep forming systems in the Atlantic, I think it is safe to say the United States is definitely at risk for further landfalls this season.