Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 6:17 AM GMT on November 09, 2012
Eastern Atlantic disturbance
An area of disturbed weather has formed in the eastern Atlantic about 500 miles west-northwest of the Cape Verde Islands. This activity is associated with a surface trough interacting with a large upper low.
Figure 1. Latest infrared satellite image of the eastern Atlantic disturbance, soon to be designated Invest 91L.
Upper-level winds are currently not favorable for significant development, but the GFS suggests that the mid-level flow will relax before the upper tropospheric flow does. In fact, according to that model, upper-level winds never quite become optimal for tropical cyclogenesis, with only a brief period of relatively light northwesterly flow from about 72-96 hours that still looks more like shear than diffluence. Subtropical entities do not generally have especially cold cloud tops, which is why the upper-level winds don't really affect them.
This system is not currently showing signs of organization, although it is producing sustained winds to near gale force as per earlier scatterometer data. However, the aforementioned data, along with surface observations, suggest that the associated wind field is rather broad, which is characteristic of a non-tropical low. Buoy 41139, located about two degrees west of the disturbance recently reported a sustained wind of 30 mph. Since this observation occurred outside the deepest thunderstorms, it is presumed that stronger winds are occurring closer to the convection, particularly in the well-defined band east of the estimated center; it also suggests that the gale force winds seen on the ASCAT pass were not rain-contaminated. Should this system ultimately acquire a name, it will likely skip the depression stage.
All available data suggests that the system currently lacks a well-defined surface wind field, with all of the closed winds found in the middle and upper levels of the atmosphere. Additionally, surface pressures are not falling.
While this system could ultimately attempt to develop, I expect that any significant development will wait until the mid-level shear starts to relax, in about 24-36 hours. Complicating matters further is a possible low pressure system that the global models (including the GFS, and to a lesser extent the Euro) forecast to from from the vigorous cold front over the western Atlantic ahead of this disturbance. While not explicitly shown in the global model forecast fields, this sort of evolution could lead to large errors in the track later in the period due to a binary interaction between the two entities.
This disturbance is expected to move slowly westward over the next day or two, before turning toward the west-northwest thereafter. This system is not expected to threaten any land areas.
Probability of development in 48 hours: 20%
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