Tropical weather analysis - May 14, 2012
Tropical Depression One-E
The first tropical depression of the season has formed, albeit a day early. It is rather unusual to get a tropical cyclone prior to the official start of the season. As far as we know, there have only been two tropical cyclones that have formed before May 15: Hurricane Alma in 1990, and an unnamed tropical storm in May of 1996. As of the latest official NHC advisory, here are the coordinates on this strengthening system:
Wind: 35 mph, with higher gusts
Location: 10.0°N 107.3°W
Movement: W at 8 mph
Pressure: 1006 mb
Category: Tropical depression (Saffir-Simpson Hurricane Scale)
Visible satellite pictures reveal that the low-level center may be moving closer to the deep convection, and the system is very likely already a tropical storm. The tropical cyclone is battling southeasterly shear as evidenced by the restricted outflow to the east, but this has not permeated the core yet. Upper-level winds appear favorable for the system to become a moderate tropical storm before becoming less favorable by Tuesday afternoon.
Figure 1. Latest infrared satellite image of Tropical Depression One-E, courtesy of NOAA's Satellite Services Division (SSD).
Water vapor imagery shows the ridge building westward ahead of the tropical cyclone. This synoptic evolution favors a continued westward motion with an increase in forward speed, although model guidance is unanimous in significantly slowing the system beyond 72 hours in response to developing cyclonic flow to the west, associated with a trough, and cyclonic flow to the east, associated with a possible tropical cyclone in the Gulf of Tehauntepec.
The GFDL and HWRF still turn the storm toward Baja, but these models are clearly overdoing the storm's response to the anomalous southwesterly flow forecast to linger in the vicinity of Baja by midweek. In addition to that, these models almost always seem to exhibit a poleward bias for Eastern Pacific systems. I fail to see why the storm will be that deep, and the ridge is stronger than what some of the models are indicating, so my forecast track remains along the southern edge of the guidance, in best agreement with the 12z run of the GFS.
This system should dissipate in about four days.
Elsewhere
Global model guidance continues to insist on another tropical cyclone developing behind TD One-E in about five to six days. This occurs as a large surge of monsoonal moisture manifests across the western Caribbean and adjacent eastern Pacific. This moisture is likely attributable to the upward pulse of the MJO moving into that area of the world. The synoptic pattern, with a 500 mb weakness in the Gulf of Mexico, favors an eventual turn to the Mexican coast, although long-range prognostications like this one are highly speculative. Regardless, this system should move slowly enough and remain in close enough proximity to the coast to deliver several days of locally heavy rains, as well as high surf along coastal areas.
On the Atlantic side of things, the GFS continues to forecast the development of a tropical storm in the western Caribbean. While theoretically this is possible given the large-scale pattern in this region (lower pressures in the western Caribbean and Gulf of Mexico downstream higher heights across the midwest and Great Lakes), I think there is simply too much energy in the Pacific for this storm to have much room to develop. Additionally, the forecast point of origin within this model is very close to Central America, another factor that could inhibit development. It is pretty unusual to get a named storm in May, much less one forming side by side another tropical cyclone. However, heavy rainfall could eventually overspread portions of south Florida, bringing welcome rains.
The models have also backed off in developing a tropical storm off the eastern seaboard. Conceivably, this would occur with a dying cold front that moves into the western Atlantic in about five days. At the very least, it is possible that a weak area of low pressure could form along the tail end of the then diffuse front. Such a system would move out to sea amidst southwesterly environmental steering flow.
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