Tropical weather analysis - May 15, 2012
Aletta
Tropical Storm Aletta was named overnight. As of the just released advisory from the hurricane center, the following was posted:
Wind: 45 mph, with higher gusts
Location: 11.2°N 110.4°W
Movement: W at 10 mph
Pressure: 1003 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)
The center remains just embedded within the of the ball of the central convection, which retains cloud top temperatures of about -80C. The cloud pattern is a little better organized than it was yesterday, with more curvature to the associated convection. The system is still undergoing easterly shear, as evidenced by the outflow pattern, where the cirrus are emanating primarily from the western quadrant.
Dry air lies just to the west, but this is not adversely affecting Aletta at this time.
Figure 1. Latest visible satellite image of Tropical Storm Aletta, courtesy of NOAA's Satellite Services Division (SSD).
Water vapor imagery shows that a weakness lies to the north of the tropical storm, over the Gulf of California and far western Mexico. Kudos to the global models, who have consistently predicted this. While I am still not calling for this to recurve Aletta, most of the global models express disagreement, with a large trough forecast to amplify to the west of the tropical cyclone. The purported weakness extends all the way down to at least 850 mb within the model forecast fields, so if this were to verify, Aletta would almost certainly feel some poleward tug. However, the cyclone is likely to slow significantly by Friday as it becomes embedded within a weak southwesterly steering regime, possibly a little sooner. It appears that this weakness has been moving Aletta a little more northward, as the storm is off by about 20 miles from the 0z forecast point.
Water vapor and CIMSS imagery shows that Aletta is headed toward a region of strong southwesterly shear. This should begin to weaken the storm by tomorrow. Indeed, the western semicircle is already being affected by this shear, with the cirrus no longer advancing westward. Also, since I expect the storm to move a bit more northerly now, this will put it closer to cooler waters that lie along 115W.
The storm still has a chance to intensify a little more before the shear sets in.
5-day intensity forecast
Initial 15/2100Z 40 KT 45 MPH
12 hour 16/0600Z 45 KT 50 MPH
24 hour 16/1800Z 40 KT 45 MPH
36 hour 17/0600Z 35 KT 40 MPH
48 hour 17/1800Z 30 KT 35 MPH
72 hour 18/1800Z 25 KT 30 MPH...remnant low
96 hour 19/1800Z 25 KT 30 MPH...remnant low
120 hour 20/1800Z...dissipated
Elsewhere
An area of disturbed weather has developed in the Gulf of Tehauntepec. Environmental conditions appear conducive for slow development of the disturbance as it moves west to west-northwest, although its large size may inhibit rapid development in the short-term.
Probability of development in 48 hours: 10%
The GFS continues to predict a western Caribbean tropical storm, and is a little more aggressive today. This system is now within the realm of one week, so it needs to be watched. I still don't think this system will amount to much, though, especially if pre-91E strengthens quicker than anticipated.
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