Tropical Storm Aletta peaks in intensity; Invest 92E forms, likely to become Bud
Tropical Storm Aletta, the first named storm of the 2012 Pacific hurricane season, has peaked and is quickly deteriorating in organization this afternoon as evidenced by visible satellite imagery. The tropical cyclones consists of an intense area of convection with substantial outflow noted on the northern side. No spiral bands exist with Aletta, likely due to the combination of moderate easterly wind shear and very dry air to the system's west. Subjective Dvorak Satellite Classifications remain unchanged at T2.5 from both TAFB and SAB, so it appears that the tropical storm will remain as such. Maximum sustained winds as of the 8 AM PDT advisory are 40 mph with a minimum barometric pressure of 1004 millibars.
Figure 1. Afternoon infrared satellite imagery of Tropical Storm Aletta.
The forecast for Tropical Storm Aletta
As aforementioned, Aletta lies in a region of moderate wind shear and dry air. This should act to quickly weaken the system over the next 24-48 hours. The official National Hurricane Center forecast has Aletta degenerating into a post-tropical/remnant area of low pressure in 72 hours; I believe that, with increased wind shear and a dry environment, the cyclone will probably become post-tropical in 36 hours or so. Aletta is expected to continue west to west-northwestward over the next 12 hours or so under the influence of a strong mid-level ridge of high pressure, but a turn towards the north and eventually northeast is likely as a weakness develops to the north of the system. It is possible that the remnants of Aletta could eventually bring rainfall to the Baja of California. My forecast for Tropical Storm Aletta is as follows:
...FORECAST MAX WINDS...
INIT 16/2000Z 35 KT 40 MPH...TROPICAL STORM
12 HR 17/0800Z 30 KT 35 MPH...TROPICAL DEPRESSION
24 HR 17/2000Z 25 KT 30 MPH...TROPICAL DEPRESSION
36 HR 18/0800Z 25 KT 25 MPH...POST TROP/REMNT LOW
48 HR 18/2000Z 20 KT 25 MPH...POST TROP/REMNT LOW
72 HR 19/0800Z 15 KT 20 MPH...DISSIPATED
96 HR 19/2000Z 15 KT 20 MPH....DISSIPATED
120 HR 20/0800Z 15 KT 20 MPH...DISSIPATED
Invest 92E forms
A westward moving area of low pressure in the East Pacific a few hundred miles east of Tropical Storm Aletta, Invest 92E, has developed and is poised to become "Bud" over the next few days. Visible satellite loops reveal a distinctive low-level spin associated with the disturbance, and Subjective Dvorak Satellite Classifications are T1.0 from both SAB and TAFB. The National Hurricane Center is currently giving 92E a Medium chance, 30%, of developing into a tropical cyclone over the next 48 hours. Given its satellite appearance and current level of organization, I am giving 92E a higher chance, 50%, of developing into a tropical cyclone over the next two days.
Figure 2. Afternoon infrared satellite imagery of Invest 92E.
The forecast for 92E
Invest 92E lies in an environment very conducive for tropical development, characterized by wind shear around 10 knots and Sea Surface Temperatures in excess of 28 °C. In addition, very little dry air is present due to the upward pulse of the MJO. This should allow the invest to gradually strengthen over the next few days, attaining tropical depression status in 36 hours or so and tropical storm status in 48 hours or so. The disturbance is expected to track northwest over the next 24 hours before briefly stalling out as a weakness passing to the north of the system. This should turn the system back towards the east before a ridge of high pressure builds across the west, forcing the cyclone towards the southeast. Yet another weakness should emerge by 120 hours out, pulling the system to the north towards the Mexican coastline, which is depicted by two of the global models, the GFS and the ECMWF. For this reason, residents living along the Mexican coastline need to pay close attention to Invest 92E and be on high alert, as the steering pattern is reminiscent of those that develop during the early and late portions of the Pacific hurricane season which are known to allow tropical cyclone hits along the Mexican coastline. My forecast for the invest is as follows:
...FORECAST MAX WINDS...
INIT 16/2000Z 25 KT 30 MPH...INVEST
12 HR 17/0800Z 25 KT 30 MPH...INVEST
24 HR 17/2000Z 25 KT 30 MPH...INVEST
36 HR 18/0800Z 30 KT 35 MPH...TROPICAL DEPRESSION
48 HR 18/2000Z 35 KT 40 MPH...TROPICAL STORM
72 HR 19/0800Z 40 KT 45 MPH...TROPICAL STORM
96 HR 19/2000Z 50 KT 60 MPH...TROPICAL STORM
120 HR 20/0800Z 60 KT 70 MPH...TROPICAL STORM