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Hurricane Season 2012: Tropical Storm Aletta (Eastern Pacific Ocean)
05.21.12
 
NASA's CloudSat Sees Fading Tropical Depression Aletta

CloudSat revealed the main convective core west of the center of Aletta's circulation. › View larger image
CloudSat revealed the main convective core west of the center of Aletta's circulation. This convective core is all that remains of the weakening Aletta. Heavy precipitation is noted by lacked of signal (attenuation) of the CPR (cloud profiling radar).
Credit: Natalie Tourville, Colorado State University
Tropical Storm Aletta, the first tropical system of the Eastern Pacific season, formed southwest of Mexico on May 11, 2012. NASA's CloudSat satellite provided a unique look at the depression as it weakened.

The system reached maximum winds of 45 knots (52 mph) on May 16th but quickly lost organization due to unfavorable tropical atmospheric conditions.

NASA's CloudSat satellite passed over Tropical Depression Aletta on May 17, 2012 at 2115 UTC (5:15 p.m. EDT) as the storm continued to diminish in strength. Winds were estimated at 30 knots (34.5 mph) with a pressure of 1006 millibars at the time CloudSat passed overhead.

Wind shear and a low pressure trough (elongated area of low pressure) moving across the area contributed to the demise of the system. Imagery from the MODIS instrument on NASA's Aqua satellite was overlaid with the CloudSat track and revealed the main convective core west of the center of the circulation (red dot). This convective core is all that remains of the weakening Aletta. Heavy precipitation is noted by lacked of signal (attenuation) of the CPR (cloud profiling radar). CloudSat's 94GHz radar signal can detect in the range of -40 dBZ to 20 dBZ.

The anvil of the system extends north and south of the system as the convective core reaches the tropopause and spreads outward. Cloud top heights reach 15-16 km (9.3 to 9.9 miles), smaller convective cumulus cells can be seen to the north and south of the system underneath the cirrus anvil top. CloudSat observations reveal the vertical distribution of water and layering of clouds not available with other conventional radars.

CloudSat recently celebrated six years since launch (April 28, 2006) and is approaching six years since the radar become operational (June 2, 2006). The satellite recently rejoined the A-TRAIN satellite constellation on May 16, 2012 after a battery anomaly in April 2011 and continues to operate during the daylight hours.

The last bulletin on Post-Tropical Cyclone Aletta was posted on May 19, 2012. Aletta was about 585 miles south-southwest of Cabo San Lucas, Mexico and was drifting east. Its remnants will continue to move east, later south.

Text Credit: Natalie Tourville
Colorado State University



May 18, 2012

Another Tropical Cyclone Developing

Tropical storm Aletta is forecast to weaken › View larger image
Tropical Storm Aletta is forecast to weaken
Credit: SSAI/Hal Pierce
TRMM data revealed very heavy rainfall in the northeastern quadrant of 92E › View larger image
TRMM data revealed very heavy rainfall in the northeastern quadrant of 92E
Credit: SSAI/Hal Pierce
This TRMM 3D image shows that a few of these strong convective storms reached heights of about 15km (~9.3 miles). › View larger image
This TRMM 3D image shows that a few of these strong convective storms reached heights of about 15km (~9.3 miles).
Credit: SSAI/Hal Pierce
While Tropical storm Aletta is forecast to weaken and dissipate another tropical cyclone appears to be forming in the eastern Pacific south of Acapulco, Mexico. The TRMM satellite passed above this tropical disturbance (92E) on 18 May 2012 at 0957 UTC. Data captured with this pass by TRMM's Microwave Imager (TMI) and Precipitation Radar (PR) instruments were used in the rainfall analysis shown. This analysis indicates that this area contained very heavy rainfall in the northeastern quadrant of the disturbance. Some storms were producing rainfall at a rate of over 50 mm/hr (~2 inches).

A 3-D image from TRMM PR shows that a few of these strong convective storms reached heights of about 15km (~9.3 miles). Radar reflectivity values of over 50 dBz found by TRMM PR in this stormy area provided more evidence that heavy rainfall was occurring. The National Hurricane Center (NHC) assigned this disturbed area a 40% probability of becoming a tropical cyclone within the 48 hours. It would be named Bud.

Text Credit: Hal Pierce
SSAI/NASA Goddard Space Flight Center, Greenbelt, Md.




























May 16, 2012

TRMM Sees Disorganized Aletta

TRMM showed Aletta producing rainfall at a rate greater than 50mm/hr (~2 inches). › View larger image
Data from TRMM's Microwave Imager (TMI) and Precipitation Radar (PR) instruments were used in the rainfall analysis shown above.
Credit: SSAI/Hal Pierce
Some of the heaviest thunderstorms within Aletta were reaching heights of about 16km (~9.9 miles). › View larger image
TRMM's PR data were also used to show Aletta's 3-D vertical structure in the image just above.
Credit: SSAI/Hal Pierce
The TRMM satellite passed almost directly above tropical storm Aletta in the eastern Pacific Ocean on 16 March 2012 at 1146 UTC. Data from TRMM's Microwave Imager (TMI) and Precipitation Radar (PR) instruments were used in the rainfall analysis shown above. Aletta's past and future positions are shown overlaid in white. Aletta looks disorganized in this orbit but some very heavy thunderstorms, producing rainfall at a rate greater than 50mm/hr (~2 inches), were located near the storm's center.

TRMM's Precipitation Radar (PR) found that some thunderstorms contained very heavy rainfall with a reflectivity value greater than 52dBZ being returned to the satellite. TRMM's PR data were also used to show Aletta's 3-D vertical structure in the image just above. This analysis shows that some of the heaviest thunderstorms within Aletta were reaching heights of about 16km (~9.9 miles). These towering thunderstorms can be a sign of intensification in tropical cyclones but dry air ingestion and wind shear in the future are expected to weaken Aletta.

Text Credit: Hal Pierce
SSAI/NASA Goddard Space Flight Center, Greenbelt, Md.















May 15, 2012

Tropical Storm Aletta Forms

TRMM image of tropical storm Aletta on 15 May 2012 at 0253 UTC › View larger image
TRMM image of Tropical Cyclone Aletta on 15 May 2012 at 0253 UTC
Credit: TRMM / Hal Pierce
The eastern Pacific hurricane season starts today. Just slightly ahead of schedule tropical storm Aletta formed yesterday well to the southwest of the Mexican coast. This image uses data captured when the TRMM satellite passed above Aletta on 15 May 2012 at 0253 UTC. TRMM's Microwave Imager (TMI) instrument had a good look at the newly formed storm and showed that Aletta had a large area of light to moderate rainfall north of the storm's center of circulation. The TMI rainfall analysis is shown overlaid on an enhanced infrared image from TRMM's Visible and InfraRed Scanner (VIRS) instrument.

Aletta's past and predicted locations with appropriate symbols are shown in white. The tropical storm is expected to intensify slightly and have it's greatest wind speeds of 45 knots (~52 mph) on May 16, 2012. Aletta is then forecast to continue moving harmlessly toward the west-northwest over open water and dissipate to a remnant low on May 19, 2012.

Text Credit: Hal Pierce
SSAI/NASA Goddard Space Flight Center, Greenbelt, Md.