Unusual… but not unprecedented… Tropical Storm Claudette formed on Saturday morning when the storm’s center was inland, about 45 miles southwest of New Orleands.

This storm has now been blamed for flooding rains… isolated storm totals up to 15 inches. It produced tornadoes and caused wind damage. There was also a 15-car pile up on I-65 in Alabama, which had multiple fatalities.

There’s no doubt this storm system packed a punch.

But most tropical storms get the named over water. Tropical systems need moisture from the ocean to form.

So Claudette’s formation is somewhat rare. Only a handful of storms, around 10 or so, have ever been recorded forming over land. To put it in perspective, only two percent of all Atlantic tropical cyclones have formed over land (1851-2015).

The last time a tropical storm formed over land here in the United States was Tropical Storm Julia back in 2016. It formed inland near Jacksonville, Florida. Julia’s the first tropical storm to get named while over land in Florida.

Because Claudette was still so close to the Gulf of Mexico, its circulation likely gathered moisture from the warm ocean waters to strengthen.

There’s also another theory. Another meteorological phenomena has been studied recently to better explain why tropical systems intensify over land is something called the Brown Ocean Effect. Studied by NASA scientists, they found that the land many storms from the past that have either formed over land or intensified over mimicked characteristics from the ocean. Things like rich soil moisture, constant surface temperatures, and the release of latent heat (aka evaporation) all contributed to storm intensification.

Either way… more research will be done. Some scientists are even saying that in post-season analysis it might be determined that Claudette actually did form just offshore, before making landfall.