Nav: Home

NASA catches Tropical Cyclone Gelena's post-tropical transition

February 15, 2019

Tropical cyclones can become post-tropical before they dissipate, meaning they can become sub-tropical, extra-tropical or a remnant low pressure area.  As Tropical Cyclone Gelena transitioned into a subtropical storm, NASA's Aqua satellite provided a visible image of the storm.

On Feb 15 at 10 p.m. EDT (Feb. 16 at 0300 UTC), the Joint Typhoon Warning Center or JTWC noted that Gelena had already become subtropical. JTWC issued their final warning on Gelena. At that time, the storm had maximum sustained winds near 40 knots (46 mph/74 kph). It was centered near 29.8 degrees south latitude and 89.3 degrees east longitude. That's 1,426 nautical miles east-southeast of Learmonth, Australia. Gelena was moving east-southeast.

What is a Post-tropical Storm? 

A Post-Tropical Storm is a generic term for a former tropical cyclone that no longer possesses sufficient tropical characteristics to be considered a tropical cyclone. Former tropical cyclones that have become fully extratropical, subtropical, or remnant lows, are three classes of post-tropical cyclones. In any case, they no longer possesses sufficient tropical characteristics to be considered a tropical cyclone. However, post-tropical cyclones can continue carrying heavy rains and high winds.

What is a Sub-tropical Storm?

 According to the National Oceanic and Atmospheric Administration, a sub-tropical storm is a low-pressure system that is not associated with a frontal system and has characteristics of both tropical and extratropical cyclones. Like tropical cyclones, they are non-frontal that originate over tropical or subtropical waters, and have a closed surface wind circulation about a well-defined center.

Unlike tropical cyclones, subtropical cyclones derive a significant proportion of their energy from baroclinic sources (atmospheric pressure), and are generally cold-core in the upper troposphere, often being associated with an upper-level low pressure area or an elongated area or trough of low pressure.

In comparison to tropical cyclones, these systems generally have a radius of maximum winds occurring relatively far from the center (usually greater than 60 nautical miles), and are generally less symmetric.

What is an Extra-tropical Storm?

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.

Visible NASA Imagery Shows the Transition

Visible imagery from NASA's Aqua satellite revealed Gelena's subtropical transition.

At 3:25 a.m. EDT (0825 UTC) on Feb. 15, 2019, the Moderate Resolution Imaging Spectroradiometer or MODIS instrument aboard NASA's Aqua satellite provided a visible image of subtropical storm Gelena in the Southern Indian Ocean.  The MODIS image showed Gelena had a closed surface wind circulation about a well-defined center, but the storm has become asymmetric (as subtropical storms do).

The Joint Typhoon Warning Center noted "animated multispectral satellite imagery shows cloud tops continuing to warm and convective structure continuing to unravel. [Another satellite] image showed remnant convective bands [of thunderstorms] sheared (pushed by winds) to the south and wrapping into an elongated partially exposed low level circulation center."

Gelena is expected to continue moving through the Southern Indian Ocean over the next day until it dissipates.
-end-
By Rob Gutro

NASA's Goddard Space Flight Center

NASA/Goddard Space Flight Center

Related Tropical Cyclone Articles:

NASA find Herold a fading ex-tropical cyclone
Former Tropical Cyclone Herold is now a fading area of low-pressure in the Southern Indian Ocean and NASA's Aqua satellite provided forecasters with a visible image.
NASA sees Tropical Cyclone Herold's eye
NASA's Aqua satellite passed over the Southern Indian Ocean and captured an image of a well-developed Tropical Cyclone Herold at hurricane strength, east of Madagascar.
A new method to improve tropical cyclone intensity forecasts
There are many reasons for model errors in numerical weather forecasting of tropical cyclone intensity.
NASA catches the dissipation of Tropical Cyclone Claudia
Tropical Cyclone Claudia was dissipating in the Southern Indian Ocean when NASA's Terra satellite captured a visible image of storm as it flew overhead in its orbit around the Earth.
NASA finds tropical cyclone 02S consolidating
NASA's Aqua satellite captured an image of Tropical cyclone 02S and the visible image showed that the storm was getting better organized.
NASA finds Tropical Cyclone's Vayu getting stretched
When NASA's Aqua satellite passed over the Northern Indian Ocean, it captured an infrared image that revealed Tropical Cyclone Vayu was elongating.
NASA takes Tropical Cyclone's Vayu's temperature
NASA's Aqua satellite passed over the Northern Indian Ocean and took the temperature of Tropical Cyclone Vayu as it moved northward in the Arabian Sea.
NASA catches development of Tropical Cyclone 02A
Visible imagery from NASA's Terra satellite provided confirmation of the development of Tropical Cyclone 02A in the Arabian Sea, Northern Indian Ocean.
NASA goes infrared on powerful Tropical Cyclone Fani
NASA's Aqua satellite focused an infrared eye on a very powerful Tropical Cyclone Fani as it approached landfall in northeastern India.
NASA finds a more circular Tropical Cyclone Lorna
NASA-NOAA's Suomi NPP satellite passed over the Southern Indian Ocean and captured a visible image of what appeared to be a more organized Tropical Cyclone Lorna.
More Tropical Cyclone News and Tropical Cyclone Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Meditations on Loneliness
Original broadcast date: April 24, 2020. We're a social species now living in isolation. But loneliness was a problem well before this era of social distancing. This hour, TED speakers explore how we can live and make peace with loneliness. Guests on the show include author and illustrator Jonny Sun, psychologist Susan Pinker, architect Grace Kim, and writer Suleika Jaouad.
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.