What’s the difference between ‘subtropical,’ ‘tropical,’ and ‘post-tropical’ storms? Melissa explains it all

We all go through changes in life, but a storm named Melissa has had quite a metamorphosis in the last few days.

When it first earned a name from the National Hurricane Center at 11 a.m. on Friday, Melissa was well off the New Jersey coast, churning up the ocean and generating storm waves that flooded roads at the Shore, with ripple effects all the way back to Philadelphia — all without a drop of rain.

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The hurricane center first declared that the swirling mass had become a “subtropical storm." (The naming of subtropical cyclones is a 21st-century development, says Dennis Feltgen, hurricane center meteorologist and communications chief; it didn’t start until 2002.)

On Saturday, Melissa was promoted to a “tropical storm,” only to be busted to “post tropical” status on Monday morning, falling into the sub-category of “extra tropical,” or E.T.

» READ MORE: Wind, waves cause some beach erosion at New Jersey shore

Since it has finished pestering the beaches and become essentially a so-called fish storm and was last seen 400 miles off Newfoundland, would fish or mammal care about such distinctions?

For the record, the hurricane center does care. So what are the differences? It comes down to the energy sources, says Phil Klotzbach, a hurricane specialist at Colorado State University.

“Tropical storms and hurricanes get their energy from warm ocean waters, while extra-tropical cyclones derive their energy from temperature gradients in the atmosphere,” he says. Those contrasts are found in the higher latitudes; not much cool air makes it to the tropics.

“Subtropical cyclones are effectively hybrid storms that have characteristics of both tropical and extra-tropical cyclones.”

Anyone who remembers Sandy can testify that technical distinctions do not speak to a storm’s severity. When Sandy made landfall just north of Atlantic City seven years ago, the hurricane center decreed that it had lost its tropical identity and had become “post tropical.”

That decision came under heavy criticism at the time and was blamed for creating a storm of confusion.

The Melissa distinctions aside, reaching an "M" name means that the Atlantic season has made it halfway through the alphabet and now has had 13 named storms. That’s two above the long-term averages for the date.

Although the season is winding down, the center says a disturbance off the African coast has a 90 percent chance of becoming Nestor in the next two days.

The latest date for a tropical storm in the Atlantic Basin, which includes the Gulf of Mexico and Caribbean Sea, is Nov. 23.