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Hernan (Eastern Pacific Ocean)
July 29, 2014

[image-78]NASA Sees Warmer Cloud Tops as Tropical Storm Hernan Degenerates

Tropical Storm Hernan degenerated into a remnant low pressure area on July 29. Infrared imagery from NASA's Aqua satellite revealed cloud tops were warming as the storm weakened. 

The Atmospheric Infrared Sounder or AIRS instrument aboard Aqua gathered infrared data on a quickly weakening Hernan on July 29 at 5:11 a.m. EDT. The data was then made into a false-colored image at NASA's Jet Propulsion Laboratory in Pasadena, California. The AIRS image showed small, fragmented areas of a few powerful thunderstorms with high, cold cloud tops in Tropical Storm Hernan as it continued weakening. For the most part, however, the cloud top temperatures warmed through the system which indicated the uplift was weaker.

By 11 a.m. EDT (1500 UTC) Hernan was no longer a tropical cyclone and had become a remnant low pressure area. The center of post-tropical cyclone Hernan was located near latitude 23.5 north and longitude 121.1 west, about 710 miles (1,145 km) west of the southern tip of Baja California, Mexico. The post-tropical cyclone is moving toward the west-northwest near 15 mph (24 kph) and this general heading with a decrease in forward speed is expected through Wednesday night, July 30. Maximum sustained winds are near 35 mph (55 kph).

The National Hurricane Center expects that remnant low to dissipate during the next couple of days.

Text credit:  Rob Gutro
NASA's Goddard Space Flight Center


[image-51]July 28, 2014 - NASA Sees Tropical Storm Hernan Near Mexico's Baja California

Tropical Storm Hernan developed over this past weekend and reached hurricane strength before vertical wind shear kicked in and kicked the storm down. NASA's Terra satellite passed over Hernan when it was developing as a tropical depression near Baja California, Mexico.

Tropical Storm Hernan was born on Saturday, July 26 at 5 a.m. EDT as Tropical Depression 8-E. By 5 p.m. EDT it strengthened into Tropical Storm Hernan. At 11 a.m. EDT on Sunday, July 27, Hernan's maximum sustained winds were already up to 70 mph, just four miles per hour shy of hurricane status. As Hernan passed west of Socorro Island at 5 p.m. EDT on July 28 it reached hurricane status when its maximum sustained winds reached 75 mph (120 kph). It remained a hurricane for about 12 hours before dropping back to a tropical storm on July 29 at 5 a.m. EDT when maximum sustained winds were near 70 mph (110 kph).

Hernan moved into an area of persistent westerly wind shear blowing at between 15 to 20 knots (17.2 to 23.0 mph/27.8 to 37.0 kph). That wind shear is deteriorating the cyclone's organization. Infrared satellite data from instruments like the Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite showed that the cloud top temperatures were warming. Warming cloud tops means that the uplift of air had weakened. Uplift is air that pushes thunderstorms into the top of the troposphere. The higher the thunderstorm cloud top, the colder it is (because the troposphere cools as you go higher). Higher, colder cloud tops in thunderstorms mean stronger thunderstorms.

Visible satellite data today indicated "a rather shapeless cloud pattern," according to the National Hurricane Center. That means the circulation is less organized. 

At 11 a.m. EDT (1500 UTC) on July 28, Tropical Storm Hernan's maximum sustained winds were down to 65 mph (100 kph). It was centered near 20.5 north latitude and 115.9 west longitude, about 420 miles west-southwest (675 km) of the southern tip of Baja California. Hernan is moving toward the northwest near 16 mph (26 kph) and is forecast to continue through Tuesday night, July 29, followed by a turn to the west. 

Forecaster Roberts at the National Hurricane Center noted today, July 28 that in addition to being battered by wind shear, "an increasingly stable air mass and decreasing sea surface temperatures should ultimately weaken Hernan into a shallow post-tropical cyclone in 48 hours."

Text credit:  Rob Gutro
NASA's Goddard Space Flight Center

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Tropical Storm Hernan
This visible image of Tropical Storm Hernan (as Tropical Depression 8E) near Baja California, Mexico was taken on July 26 at 2:05 p.m. EDT by NASA's Terra satellite.
Image Credit: 
NASA Goddard MODIS Rapid Response Team
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AIRS image of Hernan
This false-colored infrared image on July 29 at 5:11 a.m. EDT from NASA's Aqua satellite shows small, fragmented areas of a few powerful thunderstorms with high, cold (purple) cloud tops in Tropical Storm Hernan.
Image Credit: 
NASA JPL, Ed Olsen
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Page Last Updated: July 29th, 2014
Page Editor: Lynn Jenner