Tropical Storm Aletta and the first day of the 2012 Pacific hurricane season
Tropical Storm Aletta, the first named of the 2012 Pacific hurricane season, has formed in the East Pacific on what is ironically the first day of the season in that basin. As of the 8 AM PDT advisory, maximum sustained winds are estimated at 40 mph and the minimum barometric pressure is down to 1004 millibars. Visible satellite imagery reveals a recent deep burst of convection atop Aletta's well-defined circulation, and Subjective Dvorak Satellite Classifications are T3.0 from both SAB and TAFB. For this reason, I believe Aletta is a good deal stronger than earlier this morning, and likely has maximum sustained winds near 50 mph.
Figure 1. Afternoon visible satellite imagery of Tropical Storm Aletta.
The forecast for Tropical Storm Aletta
Aletta is quickly running out of time to strengthen. Water Vapor Satellite loops reveal that a large mass of dry air lies to the north and west of the tropical storm. This, in combination with increased wind shear due to a strong upper-level trough passing to the north, should act to weaken the system as it moves west into increasingly cooler waters. The official forecast calls for gradual weakening after 24 hours, with dissipation of the tropical storm expected by 120 hours. A westward track is expected as the cyclone remains south of a strong mid-level ridge of high pressure.
2012 Pacific hurricane season begins today
The 2012 Pacific hurricane season is now underway, and it is expected to be a busy one--well above average in fact. Sea Surface Temperatures in the East Pacific lie well above normal, which should act to keep the upward pulse of the MJO in the basin a great majority of time. With increased thunderstorm activity, outflow produced from those storms will act to increase wind shear across the Atlantic but provide favorable conditions for tropical development in the East Pacific. In addition, the latest ENSO update from the Climate Prediction Center shows Sea Surface Temperatures in Nino region 3.4 up to 0.0 °C. This will act to further produce favorable conditions for development in the East Pacific. Thankfully, a majority of the tropical cyclones that form in the Pacific tend to move westward away from the Mexico coastline. Once in a while however, especially in the early and late portion of the season, deep troughs can act to steer the cyclones into the coast.
Figure 2. The list of tropical cyclone names that will be used during the 2012 Pacific hurricane season and their respective pronunciations.