NOAA GOES 11 movie/NOAA-NASA GOES Project

By Rob Gutro, NASA’s Goddard Space Flight Center

This infrared Aqua satellite AIRS image shows the Low's thunderstorms (purple and blue) are getting well organized in a circular shape. Image Credit: NASA JPL, Ed Olsen

The Eastern Pacific Low pressure system forecasters have been watching since Monday, June 8, hasn’t made the leap to a tropical depression because of wind shear. It now appears that the low’s chances for becoming the first tropical depression of the eastern Pacific have dissipated, which is likely what the low will do over the weekend.

At 5 a.m. PDT (8 a.m. EDT) on Friday, June 12, that broad area of low pressure and its associated scattered showers and thunderstorms were about 850 miles southwest of the southern tip of Baja California, or 520 miles west southwest of Socorro Island, near 14.1 degrees north latitude and 118.7 west longitude. Socorro Island is a volcanic island in the Revillagigedo Islands. The island belongs to Mexico and is about 372 miles (600 kilometers) off the country’s western coast.

The National Hurricane Center noted that the satellite imagery indicated the system has become less organized than it was on June 11. In fact, the center of circulation is now becoming more “exposed” or less circular and the convective activity or building thunderstorms are becoming fewer and weaker and scattered. Microwave imagery from the early morning hours of June 12 showed that there aren’t any strong thunderstorms in the system anymore.

Image from GOES-WEST/Courtesy of NOAA-NASA GOES Project

Winds and dry air are the two factors weakening the low and tearing it apart. Strong winds from the southwest, associated with a mid-upper atmospheric trough, that is, an extended area of relatively lower atmospheric pressure to the northwest of the storm’s center. In addition, dry air ahead of that trough (located to the northeast of the eastern Pacific Low’s center) is working its way into the low. Dry air wicks away the moisture needed to build the thunderstorms in a low pressure area, and the thunderstorms make up a tropical cyclone.

The Atmospheric Infrared Sounder (AIRS) instrument on NASA’s Aqua satellite captured the fading Low pressure system in an infrared image on June 12 at 6:05 a.m. EDT. In the infrared image, the Low’s cold clouds are now several scattered areas (in blue) indicating a weak and unorganized storm.