Monday, August 12, 2013

Stalled Fronts & Tropical Systems

Stalled frontal boundaries along the Southeast Atlantic and/or Gulf coasts have often been breeding grounds or funneling mechanisms for tropical systems over the years. Having a dying/weakening frontal boundary along very warm waters, with the temperature differential between the warmth of the ocean and the "cool" aloft allows for the possibility of stuff to spin up, often bringing some sort of tropical impact to the East Coast in the form of rain (or sometimes in the case of Alicia and a few other storms, a more nasty outcome).

The front that brings us our storms on Tuesday will drift down to an Outer Banks to New Orleans position later this week, stalling out along both coasts. There is some uncertainty in how the front plays out after that but most modeling as of now keep the front (or its remnant boundary) in that general vicinity into the weekend.  Modeling has shown waves of low pressure shooting east-northeast along that front into the Atlantic, with the GFS the most consistent in showing such a scenario.  While it's unlikely that any of these develop into anything tropical at this point, the front itself will be a bit active for the Carolinas, Southeast, and Gulf Coast with plenty of heavy rainfall.

Adding insult to injury is the prospect of a tropical system later this week in the Gulf of Mexico, which may develop out of a complex of thunderstorms that have moved into the Caribbean and are located just north of the South American coast. This, or perhaps another wave farther east in the Caribbean, could be the trigger for this model hype.  It's also possible that anything tropical develops along the front itself.  Needless to say though, it's not surprising to see things perk up a bit nor is it surprising that the development would need to occur closer to the US.

The aforementioned hype from the GFS for the past couple of days or so is projected to track into and develop in the Gulf of Mexico, along the western edge of the frontal boundary, pulling northeast into the Southeastern US.  It's not the only model to show *some* sort of tropical development later this week, with the Canadian model showing development and taking that development into South Texas or Northeast Mexico.  Other modeling out there suggests in between Alabama and Mexico, with such a spread not unusual for something that hasn't developed into a tropical entity yet.

GFS modeling for possible tropical system late this week.

Prospective wind field with GFS modeled tropical system -- note the asymmetric wind field.

The question amounts to potential strength and size.  The GFS example, as it is more closely drawn to the trough and frontal zone in the Gulf of Mexico, is the "slopical" and weaker variety, with the eastern side of the storm the stronger, rainier, more moisture-heavy side as modeled. The Canadian model shows a stronger storm and a more western track due to the fact that the model shows a weaker trough in the Gulf of Mexico and the modeled system is able to avoid getting captured by the trough and thus can meander westward through the Gulf towards landfall, getting time to organize and intensify.

With the model hype, it's still days out before anything *may* develop (and the key is may...model hype does not a storm make) but with the frontal boundary lying near a Gulf and a tropical wave around, the possibility of something developing is minimum, the probability of a lot of rain in the Southeast is pretty high.