Odd 92L in the Atlantic - Another Grace situation? 5/12/12
Good afternoon and welcome to my tropical weather update for Saturday, May 12th, 2012. I wasn't expecting to write up a tropical update - but as always, who does with these kinds of systems? Today we're dealing with 92L out in the North Atlantic by the Azores. 92L is surprisingly well organized for this time of year and this far north, but it shouldn't really surprise everyone that this is happening. SST anomalies are already 1-2C above average in that area, so it's more typical of July as it is. Satellite reveals a tight, well organized core with great spiral banding, and showing a system that is already detaching from the front that it has been associated with for the past few days. It's sudden uptick in convection though is very unnatural, and it looks well on it's way to become Sub-Tropical or Tropical Storm Alberto perhaps as soon as early tomorrow.
(figure 1. 92L in the Northern Atlantic)
Sub-Tropical or Non-Tropical?
Determining whether or not this is a warm-core system or a hybrid is difficult, but most if not all the of the phase-diagrams indicate that this system is transitioning from a symmetric cold core system to a symmetric warm core system, which is what a tropical cyclone is. However, given that the wind-radius and surface pressure is so far spread out, plus it's association with the front near by (similar to Sean in 2011), it would be sub-tropical in nature.
(figure 2. Sea Surface Temperatures in the area)
Polar Low or a Tropical Cyclone - the Grace and Vince dilemma.
These systems are very rare in the Atlantic. It was first seen in 2005 with the infamous Hurricane Vince, but was once again seen in a very similar fashion to 92L - Tropical Storm Grace. In both cases, our basic understanding of tropical formations where both defied when both of these systems developed in highly unusual locations, generally considered too hostile for formations, and thrived in those environments. The dilemma exists however on how to name it. These systems are similar to Polar Lows, so determining the difference between the two is difficult. However, 92L does not meet the requirement exactly for a Polar Low, so what it is? For now, the NHC settles on it being a sub-tropical cyclone.
In any case, the NHC will be waiting for consistency to name 92L. If it continues to look like this in say 6 hours, it is probable that it could be named as soon as tonight and as late as tomorrow. 92L does not have long to live in either case, as hostile wind shear should overcome this system in 48 hours or so.
I will release a special update if 92L is named Alberto.