Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 12:47 AM GMT on May 25, 2013
An area of low pressure over the tropical Pacific several hundred miles southwest of Acapulco, Mexico remains highly disorganized, and the potential for significant development appears to be diminishing.
Figure 1. Latest infrared satellite image of Invest 91E. Image credit: NOAA's Satellite Services Division (SSD).
Visible satellite images show several mid-level circulations competing for dominance within a convectively active monsoon trough. None of these circulations are showing signs of organization, which again, is to be expected with such strong competition for inflow. There also appears to be some easterly shear over the area, along with lingering dry air. In addition, the gyre as a whole appears to have moved very little over the last few days; while there is a mid-level high over the Gulf of Mexico that would ordinarily furnish a definitive steering mechanism for this disturbance, it is straddling the 10N latitude line, and this has isolated it from any large-scale steering influences. In addition, there is a lot of discrepancy amongst the models on which way this system is going to move over the next few days; such a spread usually heralds little movement. The lack of solid movement is not going to enable this system to gain much, if any, latitude throughout the next several days, and that will also bar development potential by keeping it embedded within the monsoon trough and its associated cyclonic circulation. It is possible that whatever is left of this system will contribute some vorticity and energy to a system well to the east near the Pacific coast of Costa Rica, which the models show becoming the next tropical cyclone of the basin in a few days.
Probability of development in 48 hours: Near 0%
Costa Rica disturbance
The aforementioned disturbance about 150 miles southwest of the Pacific coast of Costa Rica is a much bigger threat for development over the next several days. The associated shower activity is currently disorganized, and minimal near the center, but that is to be expected of a tropical disturbance at this stage. I couldn't find a decent ASCAT pass, but extrapolation of what little coverage I did get showed that the low-level center is extremely ill-defined, and the cyclonic rotation seen with the system on satellite images appears to be primarily mid-level.
Figure 2. Latest infrared satellite image of the Costa Rica disturbance (far right). Image credit: NOAA's Satellite Services Division (SSD).
Examining the upper tropospheric fields within the GFS and CMC, it appears that the large-scale environment will be diffluent and of light shear, a forecast trend which appears reasonable based on analysis of water vapor images this evening. The GFS hints that the environment could become more solidly anticyclonic as the system approaches the southern coast of Mexico in about 5 - 6 days, which would be a potentially dangerous situation if we were to get an intensifying tropical cyclone making landfall.
The large-scale pattern continues to favor a gradual motion to the west-northwest at about 5 to 10 mph over the next 72 hours as the low moves along the southern periphery of the subtropical ridge over the Gulf of Mexico. After that time, the global models are in agreement that a piece of shortwave energy will amplify the jet stream over the four corners region. The associated trough is etched as moving eastward through the Rockies by the end of the period, which would allow the system to turn northwest and north toward the southern coast of Mexico. Interests along that coast from Acapulco to Puerto Angel should monitor the progress of this system over the next 5 to 7 days, as virtually all of the models show this system making landfall. There are some timing differences, naturally, but these will be resolved with time as the models come into better agreement on the synoptic patten and the amplitude of the purported western United States trough.
Probability of development in 48 hours: 20%
Early June western Caribbean development still possible
Although during the last several cycles the operational GFS dropped the tropical cyclone it had in the western Caribbean during the June 3 - 4 timeframe, its respective ensembles, as well as the Canadian ensembles, continue to forecast a large-scale pattern that is conducive for lowering pressures in the western Caribbean during the first week of June. The forecast of this possible development may be inconsistent (in fact, I would actually expect it to be, since again, the global models tend to have notorious difficulty and struggle in correctly resolving the climatological increase in convection across this region this time of year), but the timing appears to be steadily improving, and, more importantly, the ensembles have remained remarkably consistent on a synoptic situation conducive for lower pressures across this region during that timeframe.
At the very least, it appears that an increase in moisture is on tap for the region over the next 7 - 10 days, but what, if anything, will come of that remains to be seen.
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