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A Difficult Forecast

Our unnamed storm off the coast of South Carolina is looking quite impressive on satellite images this morning, as there has been more intense thunderstorm activity over the past few hours (Figure 1). This is primarily due to the low levels of the atmosphere being warmed and moistened by previous thunderstorm activity.

NHC, however, does not think much of the recent activity. I guess that's why they are the experts and I'm a graduate student.


Figure 1. Visible (top) and infrared (bottom) satellite images for the unnamed storm off the coast of the South Carolina. Note the yellows in the infrared image indicating colder, and therefore more intense, thunderstorm tops (Courtesy NHC).

Looking at the wind field for our storm, it appears that winds have slackened this morning (Figure 2). However, this was caused by the storm moving away from a strong high pressure system that is parked over the Northeast. Because of the movement of the storm, pressure is changing less quickly with distance, and hence the winds are getting weaker.

All that said, there are still some rain-obscured observations of 50 knots (~55 mph), which probably means there are actually winds of 40-45 knots (~45-50 mph).

Figure 2. QuikSCAT image from this morning showing the wind field of the unnamed storm (Courtesy NESDIS).

So, what does the future hold for the storm? According to the computer models, not a long one (Figure 3). Most of the models are killing the storm off within 48 hours. However, my research group is in the process of showing that models do not handle extratropical transition (going from a tropical system to an extratropical system) well. I wonder if the same can be said of tropical transition?

Figure 3. UKMET forecast for the unnamed storm. The "C" indicates its current position and the "Z" indicates its final position. Notice that the storm is forecasted to be dead in 48 hours. This is consistent with the other models as well (Courtesy Bob Hart at Florida State).

At this point, without having much knowledge of how the models handle tropical transition, I would tend to believe them that the storm will soon start to weaken. This is something that bears watching the rest of the day, however, because if the thunderstorm activity continues to intensify, the storm will become stronger. If the recent burst of activity is short-lived, the storm should weaken as forecast by the models.

Stay tuned to the StormTrack for more!

Posted by Adam Moyer | Permalink