Hernan – Eastern Pacific Ocean

Aug. 28, 2020 – NASA Terra Satellite Examines Tropical Storm Hernan’s Relocated Center 

NASA infrared imagery revealed a burst of strength in Tropical Storm Hernan, located over the Gulf of California. At 12:30 a.m. EDT, NOAA’s National Hurricane Center or NHC noted that recent satellite-based wind data indicated Hernan was located northeast of previous estimates.

Terra image of Hernan
On Aug. 28 at 1 a.m. EDT (0500 UTC) the MODIS instrument that flies aboard NASA’s Terra satellite revealed the most powerful thunderstorms (yellow) minus 80 degrees Fahrenheit (minus 62.2 degrees Celsius) near Hernan’s center and over the Gulf of California. Surrounding that area were cloud top temperatures were as cold as (red) minus 70 degrees Fahrenheit (minus 56.6. degrees Celsius). All of those areas were generating heavy rain. Credit: NASA/NRL

The body of water located between the Baja California Peninsula and the Mexican mainland is known as the Gulf of California. It is a marginal sea of the Pacific Ocean.

NHC noted late on Aug. 27, that Hernan appeared poorly organized, and despite a burst of strength, the storm weakened to a depression.

Infrared Data Provides a Temperature Check

Infrared data provides temperature information, and the strongest thunderstorms that reach highest into the atmosphere have the coldest cloud top temperatures.

On Aug. 28 at 1 a.m. EDT (0500 UTC), the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA’s Terra satellite captured an infrared image of cloud top temperatures in Hernan that showed what appears to be its final burst of strength. MODIS found the powerful thunderstorms that developed were as cold as or colder than minus 80 degrees Fahrenheit (minus 62.2 degrees Celsius) near Hernan’s center and over the Gulf of California. Surrounding that area were cloud top temperatures were as cold as minus 70 degrees Fahrenheit (minus 56.6. degrees Celsius). All of those areas were generating heavy rain, but within a couple of hours, they diminished.

Hernan Weakened to a Depression

The National Hurricane Center (NHC) noted at 5 a.m. EDT that Hernan had weakened to a depression and strong thunderstorms had weakened. NHC said, “Shortly after the release of the previous advisory, microwave imagery from a WindSat overpass showed no indication of a well-defined center near Hernan’s estimated location. However, there was a hint of a small vortex well to the northeast. Confidence is therefore fairly high that Hernan has persisted as a tropical cyclone, at least through 12 a.m. EDT (0400 UTC) this morning.” WindSat is the primary instrument aboard the Coriolis mission satellite, which is jointly sponsored by the U.S. Dept. of Defense Space Test Program and the U.S. Navy.

Hernan’s Status on Aug. 28, 2020

At 11 a.m. EDT (1500 UTC), the center of Tropical Depression Hernan was located near latitude 23.4 north, longitude 109.1 west, about 60 miles (100 km) northeast of the southern tip of Baja California, Mexico. The depression is moving toward the west-northwest near 21 mph (33 kph) and this motion is expected to continue through tonight.  Maximum sustained winds have decreased to near 35 mph (55 kph) with higher gusts. Additional weakening is forecast, and Hernan is expected to degenerate to a remnant low-pressure area tonight.  The remnants are expected to dissipate on Saturday. The estimated minimum central pressure is 1006 millibars.

Forecast from NHC

Based on decreasing satellite intensity estimates, Hernan was downgraded to a tropical depression.  Additional weakening is forecast, and Hernan is expected to degenerate to a remnant low pressure area as it moves over the Baja California peninsula later today and tonight.  The system is then expected to weaken to a trough (elongated area of low pressure) on Saturday.

NASA Researches Earth from Space

For more than five decades, NASA has used the vantage point of space to understand and explore our home planet, improve lives and safeguard our future. NASA brings together technology, science, and unique global Earth observations to provide societal benefits and strengthen our nation. Advancing knowledge of our home planet contributes directly to America’s leadership in space and scientific exploration.

For updated forecasts, visit: www.nhc.noaa.gov

By Rob Gutro 
NASA’s Goddard Space Flight Center

Hernan – Eastern Pacific Ocean

Aug. 27, 2020 – A Nighttime View of Tropical Storm Hernan from a NASA-NOAA Satellite

Nighttime imagery from NASA-NOAA’s Suomi NPP satellite revealed the Eastern Pacific Ocean’s Tropical Storm Hernan along the coast of western Mexico. By the weekend, Hernan is expected to absorb nearby Tropical Storm Iselle.

Suomi NPP image of Hernan
NASA-NOAA’s Suomi NPP satellite passed the Eastern Pacific Ocean overnight on Aug. 26 at 10 p.m. EDT (Aug. 27 at 0000 UTC) and captured a nighttime image of Tropical Storm Hernan along the western coast of Mexico. Credit: NASA Worldview, Earth Observing System Data and Information System (EOSDIS)

Tropical Depression 13E formed by 5 a.m. EDT on Aug. 26 in the Eastern Pacific. Twelve hours later it strengthened to a tropical storm and was renamed Hernan.

NASA’s Night-Time View

The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard Suomi NPP provided a nighttime image of Hernan on Aug. 26 at 10 p.m. EDT (Aug. 27 at 0000 UTC).

At 5 a.m. EDT on Aug. 27, the National Hurricane Center noted, “Although Hernan is a sheared tropical cyclone, another strong burst of deep convection with cloud tops of minus 83 to minus 86 degrees Celsius has developed near and south through west of the center.” NASA research has shown that cloud tops that cold have the ability to generate heavy rainfall. By 11 a.m. EDT, first light visible satellite imagery reveals that Hernan remains a sheared tropical cyclone with most of the deep convection confined to the western semicircle.

Hernan’s Status of Aug. 27

At 11 a.m. EDT (1500 UTC) NOAA’s National Hurricane Center noted the center of Tropical Storm Hernan was located near latitude 19.1 degrees north and longitude 106.2 degrees west. That is 95 miles (155 km) southwest of Cabo Corrientes, Mexico. Hernan was moving toward the north-northwest near 5 mph (7 kph). Maximum sustained winds are near 45 mph (75 km/h) with higher gusts. The estimated minimum central pressure is 1001 millibars.

Hernan’s Forecast Track

NHC predicts Hernan will turn to the northwest, along with an increase in forward speed is expected to occur by tonight. A turn to the west is forecast this weekend. On the forecast track, the center of Hernan, along with the strongest winds and heaviest rains, is expected to remain just offshore of the southwestern coast of Mexico. Nearby Tropical Storm Iselle is expected to begin weakening on Friday, and the system is forecast to degenerate into a remnant low-pressure area on Saturday. Iselle’s remnants are expected to be absorbed by the circulation of Hernan to its west on Sunday.

About NASA’s EOSDIS Worldview

NASA’s Earth Observing System Data and Information System (EOSDIS) Worldview application provides the capability to interactively browse over 700 global, full-resolution satellite imagery layers and then download the underlying data. Many of the available imagery layers are updated within three hours of observation, essentially showing the entire Earth as it looks “right now.”

NASA Researches Earth from Space

For more than five decades, NASA has used the vantage point of space to understand and explore our home planet, improve lives and safeguard our future. NASA brings together technology, science, and unique global Earth observations to provide societal benefits and strengthen our nation. Advancing knowledge of our home planet contributes directly to America’s leadership in space and scientific exploration.

For updated forecasts, visit: www.nhc.noaa.gov

By Rob Gutro 
NASA’s Goddard Space Flight Center