The calendar reads December 9th, yet we're able to discuss a tropical-like invest feature in the Atlantic basin? What kind of strange world are we living in?
Anyway, Hovmoller diagrams suggest that this has evolved from the interaction of a tropical wave with an upper-level low in the subtropics about 5 days ago. It has moved progressively westward ever since, gradually becoming more organized and slowly working its way down to the surface. Here's a link to the SSD satellite floater over 94L. There are some similarities with this disturbance to those we saw after the end of the season in 2005, mostly in terms of initial origin and position with respect to an upper low, but they end there.
On satellite imagery, it appears to be fairly well organized, albeit favoring its northern side in terms of convection. This is due to its location with respect to a TUTT cell currently located south of the Mona Passage, aiding in diffluence aloft north of the trough axis but also punching in a bit of dry air south of there.
This evening's QuikSCAT doesn't suggest a surface circulation as of yet; however, a well-defined trough axis does appear. Note that this is a tighter turning of the winds than seen this morning. Also note that the ambiguities seem to do a pretty good job of confirming the choice of wind directions.
SSTs are approximately 27C in the region, particularly below about 24-25N.
What does the future hold for our disturbance? In the short-term, the interplay between the upper low in the Caribbean and the mid-level circulation associated with the disturbance will help determine whether or not the circulation can work its way down to the surface. It is in the most favorable region of an upper low for this type of tropical cyclone development -- the diffluent northeast quadrant, relatively far from the center of the upper low -- but can we get enough of a convective burst to stretch the vorticity and get the circulation to the surface? Given recent history, I would tend to say yes, probably occurring sometime tomorrow. In the longer-term, global models are pretty unanimous in building a strong mid- to upper-level ridge across the southeast US and southwest Atlantic basin. What happens to that upper low -- the various global model solutions from 12z today have its vorticity merging with that of 94L, which seems somewhat unrealistic -- and how strong that ridge gets will determine the medium-range evolution of this disturbance.
My thinking as of now is that the upper low will slowly slide westward while 94L pivots around its north side between it and the building subtropical ridge, steering the disturbance on a generally westward course. This will tend to limit the diffluence and synoptic-scale forcing atop the disturbance, though it may not matter much if the disturbance can get organized at the surface before this occurs. (Think of it sorta akin to a critical development threshold.) It will be a close call as to whether or not this disturbance stays north of Hispaniola and/or Cuba; my current thinking is that it will do so, but just barely as I don't think the ridge will be quite strong enough to force it on a south of due west course. Ultimately, one of the week's forthcoming eastern US storms should either capture it or tear it to shreds.
Some development is not out of the question from this disturbance -- I'm thinking weak to moderate tropical storm at most. Wind shear will be relatively low, SSTs are relatively warm north of the Greater Antilles, and there is already something there to focus upon for continued organization. A track toward the central Bahamas seems most likely; slightly further north if it develops a tad more, slightly further south of it does not. It's too early to speculate beyond that.
--------------------
Current Tropical Model Output Plots
(or view them on the main page for any active Atlantic storms!)
|
Previous
Index
Next
Flat
Re: Post Season... Watch Disturbance Northeast of the Caribbean
Edit
Reply
Quote
