Gretel – Southern Pacific Ocean

Mar. 16, 2020 – NASA Finds Gretel Becoming Extra-Tropical

NASA’s Terra satellite passed over the Southern Pacific Ocean and captured an image of Tropical Storm Gretel as it was transitioning into an extra-tropical cyclone, northwest of New Zealand.

Terra image of Gretel
On March 16, the MODIS instrument that flies aboard NASA’s Terra satellite took this image of Tropical Cyclone Gretel and showed a transitioning storm northwest of New Zealand. Credit: NASA Worldview

Tropical Cyclone 23P formed on March 14 at 4 p.m. EDT (2100 UTC) between Australia and New Caledonia. Once it intensified into a tropical storm, it was renamed Gretel.

On March 16, the Moderate Resolution Imaging Spectroradiometer or MODIS instrument that flies aboard NASA’s Terra satellite provided forecasters with a visible image of Tropical Cyclone Gretel. The bulk of Gretel’s clouds and storms were south and southeast of the center of circulation. Clouds associated with Gretel extended to northern New Zealand, despite the storm’s center being hundreds of miles away.

At 11 p.m. EDT on March 15 (0300 UTC on March 16), the Joint Typhoon Warning Center or JTWC issued the final warning on Gretel. At that time, the center of Tropical Cyclone Gretel was located near latitude 26.6 degrees south and longitude 169.7 degrees east, about 675 nautical miles north-northwest of Auckland, New Zealand. Maximum sustained winds were near 50 knots (58 mph/93 kph) and Gretel was speeding southeast at 25 knots (29 mph/46 kph).

The Joint Typhoon Warning Center or JTWC noted that Gretel will continue to move southeast and is now becoming extra-tropical.

Often, a tropical cyclone will transform into an extra-tropical cyclone as it recurves toward the poles (north or south, depending on the hemisphere the storm is located in). An extra-tropical cyclone is a storm system that primarily gets its energy from the horizontal temperature contrasts that exist in the atmosphere.

Tropical cyclones have their strongest winds near the earth’s surface, while extra-tropical cyclones have their strongest winds near the tropopause – about 8 miles (12 km) up. Tropical cyclones, in contrast, typically have little to no temperature differences across the storm at the surface and their winds are derived from the release of energy due to cloud/rain formation from the warm moist air of the tropics.

Tropical cyclones/hurricanes are the most powerful weather events on Earth. NASA’s expertise in space and scientific exploration contributes to essential services provided to the American people by other federal agencies, such as hurricane weather forecasting.

By Rob Gutro
NASA’s Goddard Space Flight Center

Lorena – Eastern Pacific Ocean

Sep. 23, 2019 – NASA Catches Tropical Storm Lorena’s Landfall Approach

As Tropical Storm Lorena was nearing landfall in northwestern Mexico, NASA-NOAA’s Suomi NPP satellite provided forecasters with an image of the storm. By Monday, Sept. 23, Lorena’s remnants were affecting the southern U.S. and bringing heavy rainfall to Arizona.

Suomi NPP image of Lorena
NASA-NOAA’s Suomi NPP satellite passed over Tropical Storm Lorena as it was approaching landfall in northwestern Mexico on Sept. 21 at 4:42 p.m. EDT (2042 UTC). Credit: NASA Worldview, Earth Observing System Data and Information System (EOSDIS)

Visible imagery from NASA satellites help forecasters understand if a storm is organizing or weakening. The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard Suomi NPP provided a visible image of Lorena on Sept. 21 at 4:42 p.m. EDT (2042 UTC).

The shape of a tropical cyclone provides forecasters with an idea of its organization and strength, and NASA-NOAA’s Suomi NPP satellite provided a visible image of the storm to forecasters as its center was approaching landfall. The storm already appeared elongated from south to north after its northeastern side had begun moving over the high terrain of northwestern Mexico. Lorena made a slow track to the coast and made landfall about 12 hours later.

Lorena’s Final Advisory

At 11 am EDT on Sunday, Sept. 22, NOAA’s National Hurricane Center issued the final advisory on the system. By that time, Post-Tropical Cyclone Lorena crossed the coast of northwestern Mexico in the morning. The center of the disturbance was estimated near latitude 28.8 degrees north and longitude 111.5 degrees west. The post-tropical cyclone was moving toward the north near 9 mph (15 kph). Maximum sustained winds associated with this system are near 30 mph (45 kph) with higher gusts.

After landfall, Lorena’s remnant clouds and rain moved north into Arizona.

Lorena’s Remnants in Arizona on Sept. 23

NOAA’s Weather Prediction Center College Park, Md. reported, “Moisture from the remnants of Lorena will contribute to heavy rain, strong to severe thunderstorms and possible flooding across the Southwest through Tuesday. There should be enough moisture in place to support a significant rainfall event with widespread 1 to 2 inch rainfall totals with much higher amounts locally, with the greatest amounts in central and southern Arizona.  This degree of rainfall warrants flash flood concerns, and a Moderate Risk of excessive rainfall is in effect for that region.  Some strong to severe thunderstorms will also be possible.”

Hurricanes are the most powerful weather event on Earth. NASA’s expertise in space and scientific exploration contributes to essential services provided to the American people by other federal agencies, such as hurricane weather forecasting.

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

By Rob Gutro 
NASA’s Goddard Space Flight Center