Natural Disasters

Tropical storms Marco, Laura head for the Gulf of Mexico, spark Fujiwhara effect scare

Simultaneous formation of two storms in western Atlantic Ocean creates Fujiwhara effect scare, that happens when 2 hurricanes combine to form a mega hurricane

By Akshit Sangomla
Published: Monday 24 August 2020

Two tropical storms, formed in the western Atlantic Ocean at nearly the same time, are likely to impact the Gulf of Mexico, sparking concerns of the rare Fujiwhara effect that occurs when two hurricanes combine to form a mega hurricane. The last time two tropical storms formed at the same time and struck the region was in 1933.

Tropical storm Marco had strengthened to a category I hurricane on August 23, 2020, but fizzled out a little overnight and downgraded to a tropical storm, according to the latest update from the United States (US) National Hurricane Centre (NHC).

Marco is the 13th named storm of the Atlantic hurricane season which runs from June to November. It is likely to make landfall along the Louisiana state coastline August 24 evening. Tropical storm Laura is the 12th named storm of the season and is currently hovering over the Caribbean.

This makes Marco and Laura the earliest 13th and 12th named storms respectively in the recorded history of Atlantic Hurricane season. Their simultaneous formation in the western Atlantic Ocean created a Fujiwhara effect scare.

The US National Oceanic and Atmospheric Administration (NOAA) said the effect occurs “when two hurricanes spinning in the same direction pass close enough to each other, and begin an intense dance around their common center. If one hurricane is a lot stronger than the other, the smaller one will orbit it and eventually come crashing into its vortex to be absorbed.”

Further, “the storms closer in strength can gravitate towards each other until they reach a common point and merge, or merely spin each other around for a while before shooting off on their own paths.”

It added:

But often, the effect is additive when hurricanes come together, and we usually end up with one massive storm instead of two smaller ones.

This generally occurs when the hurricanes pass really close to each other but the effect can have other implications when the storms are at a distance. The two current storms are likely to undergo a mild Fujiwhara effect with changes in expected tracks for both of them.

Tropical storm Marco would have already moved inland when Laura arrives, due to which the likelihood of a mega storm formation would be low. The last time a proper Fujiwhara effect happened was in 2009 in the Philippine Sea, when typhoons Parma and Melor interacted with each other.

There are other peculiarities of the Atlantic Hurricane season this year. Tropical storm formation started much earlier than usual and has also been much more active. The first named storm in the season was formed on May 16.

According to NHC, there are usually four named storms in the Atlantic Basin, which comprises the Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico, by August 23. There have been, however, more than thrice as many storms by the time this year.

Laura is currently over the Dominican Republic, Haiti and Jamaica, where it has caused heavy rainfall and flooding. The storm is on its way to Cuba, after which it will enter the Gulf of Mexico where it will gain strength on Tuesday and Wednesday ending up as a category III hurricane, making it much stronger than Marco.

The NHC has forecast that its track would be similar to tropical storm Marco and that it would also make landfall along the Louisiana coastline with impact on Texas as well. The fact that the same state is being hit by two tropical storms in quick succession is also unprecedented.

The major concern with back-to-back storms (in this case a tropical storm and a hurricane) is massive storm surges, which could inundate coastal areas and push river waters inland.

Marco could cause a surge of one-two metres above the mean sea level; the surge for Laura could be even higher. A storm surge is a rise in sea level that occurs during tropical storms, cyclones and hurricanes.

The surge causes large-scale flooding and brings saline water into agricultural fields and people’s homes, leading to long-term damage, including a decrease in soil quality. Another threat from the storms is of heavy rainfall which could range from 10-15 centimetres in the coastal areas.

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