Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 3:54 AM GMT on May 05, 2014
Although we are still technically 11 days from the official start of the eastern north Pacific hurricane season of 2014, already there are signs of an area of disturbed weather. This disturbance has been tracked by the global model fields rather well over the last few days, and those models suggest the potential for the formation of at least a broad low pressure area. The CMC and GFS are the most aggressive, calling for the system to become a mid-range tropical storm.
Satellite images show a widespread area of cloudiness and thunderstorms stretching from roughly 115W to 95W and south of 15N to approximately 5N. The National Hurricane Center (NHC) analyzes a 1010 mb surface low within the western portion of the disturbance near 9N 111W. CIMSS vorticity and satellite data suggest that this disturbance is large and disorganized, with the 1010 mb low attempting to compete with another area of rotation to the east, near 9N 105W. While the actual surface low is officially analyzed at the more westward location for now, I am led to believe the eastern area will become the dominant feature; satellite images show a distinct area of convection in this general area, perhaps a primitive convective band, with last light low cloud lines -- complimented by the transition to nighttime shortwave infrared imagery -- also suggesting a stronger cyclonic signature within this area. Water vapor animations show cirrus emanating westward and northwestward away from the more eastern area while outflow in connection with the western area looks more restricted by the upper-level cyclonic circulation to the northwest.
Figure 1. Latest infrared satellite image of the disturbance. It hasn't been designated an invest yet, so unfortunately there is no floater. The disturbance is in the lower right corner of the image. The actual 1010 mb low analyzed by the National Hurricane Center (NHC) as of 0z is actually in the lower left portion of the disturbance. But as noted above, I anticipate the development of the eastern area more strongly given current convective trends.
The aforementioned trough appears to be retrograding northward pending the arrival of a second trough off the California coast. This should cause a temporary reduction in the already improving vertical wind shear over the area. In about 48 hours, the global models show the trough amplifying and digging southward, increasing southwesterly shear over the disturbance while also slowly lifting it northward and northeastward. In the meantime, movement of this disturbance is likely to be slow, perhaps a slow drift to the west-northwest (or north-northwest if the western low dominates). There are some differences amongst the models as to which area becomes the dominant one, with the GFS, CMC, and NOGAPS favoring formation of the eastern system, while the ECMWF is infatuated with the idea of the western low consolidating. Again, given current trends, I prefer the GFS solution. If the western low dominates, the system would likely arrive to the coast about a day or two faster. In addition, the more eastward low coalescing first would also allow the system to avoid the strongest shear and cooler waters that it would otherwise encounter along the forecast track.
I am not going to get explicit with tropical cyclone development until I see which low dominates, and how the upper-level pattern ahead of the system evolves. The models don't agree either, so I'm not just rambling unreasonably.
Regardless of development, the disturbance will spread heavy rainfall, gusty winds, and localized flooding to portions of the southern coast of Mexico by midweek. Interests there should monitor its progress, since nature is apparently oblivious to summer vacationers in the Acapulco area.
Probability of development in 48 hours: 20%
Probability of development in 120 hours: 50%
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