Western Caribbean Disturbance:
The feature in the Western Caribbean I have been closely watching has, interestingly enough, developed and maintained a low-level circulation center (LLC). It is clearly evident in visible imagery:
There is no convection over the LLC, which means it probably won’t maintain itself for much longer and will probably degenerate into a trough of low pressure again. There is some convection that is displaced to the SE of the LLC due to a hefty 30 knots of wind shear as analyzed at 21Z by CIMSS:
Wind shear in excess of 25 knots is very unfavorable for tropical cyclone development. If the upper-level air forecast of the 12Z GFS verifies, then anything that does develop here won’t have much room to intensify. Steering currents would try and pull anything here to the NE, where shear is in excess of over 70 knots. Anything that would move into the Gulf of Mexico or SW Atlantic would get ripped to shreds.
While it is definitely an interesting feature to watch, I just think there is too much going against this disturbance for it to become our first tropical cyclone of the 2012 season.
Possible Subtropical Storm of the Carolina Coast:
The computer models have been very wishy-washy over the past few days in regards to the development of a possibly subtropical cyclone off the coast of North Carolina and the Mid-Atlantic states. An upper-level low (ULL) is in the process of cutting off right off the coast of North Carolina. It can clearly be seen on water vapor imagery:
Notice how the dry air is wrapping around on the south side of the low. The low is splitting from the trough just to the east. The models have been hard to interpret in terms of whether this low will try to work its way down to the surface or if another separate low will try and develop in about 2-3 days, just east of this ULL. The 12Z GFS showed a second low developing and racing off to the NE into the Canadian Maritimes while it kept the ULL lingering around just offshore North Carolina. The 12Z UKMET develops a surface low in the next day or two and moves it into North Carolina in about 72 hours. The 12Z Euro tries to do something similar to the UKMET, but once it moves the low into NC, it appears that the low then moves back out over water to the NE.
In all these model runs, the phase diagrams show that the low will be borderline warm core. Here is an example from the 12Z Euro:
Symmetric warm core low-pressure systems are tropical cyclones. For this run, the Euro is showing that the low will be a tropical or subtropical cyclone.
Sea-Surface temperatures are not warm enough to support a tropical cyclone. Typically a value of 26 degrees C is needed. However temperatures are currently around 24-25 degrees C, which is warm enough for subtropical cyclogenesis.
In addition, the computer models are not showing a favorable upper-level pattern for intensification. If anything does develop I have a hard time seeing max sustained winds any stronger than 50 mph.
Needless to say, there is a ton of uncertainty with the evolution of this low, or possibly even multiple lows. The computer models are notorious for their poor handling of cut-off lows and this is a good example. Hopefully over the next couple of days we will have a better idea of the evolution of this set-up.
Any interests in North Carolina and up the Eastern Seaboard of the U.S. as well as the Canadian Maritim Provinces should stay tuned.