© NASA WorldviewHigh-resolution visible image from the Suomi NPP satellite of the Mediterranean Sea tropical cyclone on October 30, 2016.
A tropical storm formed Halloween weekend, not in the typical Atlantic or Pacific, but in the Mediterranean Sea.
This rather strange sequence of events began as an area of low-pressure dropped southward from southern Europe and became temporarily left behind by the jet stream over the central Mediterranean Sea south of the Italian coast.
By Saturday, Oct. 29, a non-tropical low pressure center formed east of Malta, a group of islands between Sicily and the coast of Libya over the weekend.
The next day, thunderstorms became more clustered near the low-pressure center to warm the mid levels of the atmosphere sufficiently to morph the system into a subtropical storm.
A subtropical storm displays features of both tropical and non-tropical systems, including a broad wind field, no cold or warm fronts, and generally low-topped thunderstorms displaced from the center of the system.
Soon after, the clusters of storms became even more tightly concentrated, and the atmosphere warm enough that this low actually became a tropical storm.
This Mediterranean tropical storm, known as invest 90M, wasn't nearly the powerhouse deep tropical cyclone you would see in the tropical Atlantic or Pacific basins.
Its warm air was relatively shallow, but there, according to an analysis from Florida State University.
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