The Regional Delegate of the Portuguese Institute of the Sea and the Atmosphere (IPMA) has confirmed that Storm Oscar is known as an ‘Atmospheric River,’ with the region being affected by this type of storm only 5 or 6 times in the last 60 years. They typically occur during May and June.
“These storm conditions are not common but they are nothing new,” said Victor Prior, noting that this depression “is complex because it has several associated nuclei, with hot and cold frontal surfaces. It’s a mix, let’s say, of many factors.” The storm will also influence the state of the weather on the continent from Wednesday but with less intensity. In Madeira, the rest of the week will register some instability and showers, but nothing to worry about compared to the situation that is expected for the next few hours.
Atmospheric rivers were first named in the 1990s to describe a narrow moisture plume. Typically, atmospheric rivers are thousands of kilometres long and only a couple of hundred kilometres wide. These plumes typically carry more water than the Amazon River. Usually, there are 2 to 3 of these weather conditions across the globe, but with global warming, their intensity and prevalence are expected to increase. Atmospheric Rivers usually occur along the west coast of America and Western Europe.
These weather fronts should never be underestimated, as a category five (exceptional) Atmospheric River that occurred in December 1996 and lasted until the 2nd of January 1997 (100 hours), caused in excess of 1 billion dollars worth of damage. However, their absence is now thought to be linked to droughts in Spain, Portugal, and South Africa.
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