Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 10:36 PM GMT on June 13, 2010
Analysis began near 5:30 PM EDT
Invest 92L remains quite vigorous across the eastern tropical Atlantic, having survived the overnight hours. This is a true testament to its persistence, as most waves quickly fizzle out within just a day or so after displaying some vigor, even during the peak of the season. Even more remarkable it is that we are experiencing something like this during only the second week of June!
The last of the visible satellite animation loops, along with shortwave infrared satellite loops suggest that the center is located near 8N 37W. This is a rather low latitude, and few tropical cyclones have developed this far south historically. However, these same loops also indicate that the circulation is still quite broad and elongated. Current 850 mb vorticity data also strongly suggests this, with another cyclonic vorticity maximum depicted very near 40W. This particular gyre appears rather weak and disorganized compared to the stronger one to the east, near 37W, and so I am certainly not expecting this circulation to become the dominant one. Deep convection is also considerably lacking near this circulation, further suggesting that the 37W circulation will remain the dominant gyre.
Figure 1. Latest infrared shortwave IR of Invest 92L. Notice the well-defined spiral banding pattern as well as the large and well-organized upper-level anticyclonic outflow pattern aloft. This indicates that the wave's structure is well-organized, unusually so for June, or even July in this part of the Atlantic.
Though presently, deep convection is rather nil near the estimated center position, the convection within the vicinity of the center appears to be taking on a banded appearance, attempting to gradually band into the center, which indicates increasing organization. In fact, the current structure of well-defined spiral banding and minimal convection near the center is very typical of a tropical cyclone in its formative stages, though it obviously still needs more persistent deep convection, as well as a larger coverage of it, in order to be classified. Dry air is certainly not a problem for 92L, as animation of water vapor imagery indicates a large plume of moisture surrounding the system, as does CIMSS total precipitable water values, with a substantial increase in moisture coverage in just a single day.
Vertical shear is currently light over the system, only 5-10 kt, out of the south. This pattern is especially conducive for continued deepening of 92L. Additionally, a weak anticyclone appears to be centered near the estimated center of 92L, aiding in ventilation of the system. Models suggest that the shear will remain low throughout the next 48 hours, at which point it will increase sharply in association with a persistent TUTT draped across the central Caribbean. This should begin to weaken the system by that point, and it should dissipate well before reaching the central or northern Leeward Islands in the next 5 days or so. However, locally heavy rainfall and strong gusty winds will be a likelihood across those islands as the wave tracks in that general vicinity by that time. All in all, the steering pattern hasn't changed appreciably since this time yesterday, and my current thinking is still that the system eventually moves through the central Leeward Islands.
Current movement is estimated to be slowly WNW, and models suggest this motion should continue throughout the period, albeit with oscillations both north and south. The 12z NOGAPS depicted a track straight WNW, and very close to the central Leeward Islands. I believe that this is the best solution for now, though I am ever so slightly further south in my own forecast.
I do believe this will become a tropical depression in about 12 to 18 hours. However, it is only has a very short window of opportunity with which to intensify. Both the GFDL and HWRF dissipate this system well before reaching the islands. It should be noted that the further south or north the system tracks, the less shear it will encounter, as opposed to what it will if it continues moving straight WNW.
Synopsis in layman's terms
An unseasonably strong tropical wave located in the eastern Atlantic several hundred miles southwest of the Cape Verde Islands continues to display signs of organization. A tropical depression could form from this area over the next day or so before upper-level winds become unfavorable for additional development. I am expecting this system to become a tropical depression sometime tomorrow morning.
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