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Frenzy of tropical activity in Pacific could create rare weather phenomenon

AccuWeather logo AccuWeather 8/1/2021 Jessica Storm

A cluster of tropical activity has developed across the Pacific Ocean, as three features battle for dominance and hold the potential for a phenomenon called the Fujiwhara Effect to occur.

"Tropical activity has picked up across the eastern Pacific," said AccuWeather Meteorologist Alex DaSilva.

The three main areas of interest are Tropical Rainstorm 9-E, Hurricane Hilda and an area of low pressure to their east.

The good news is that all three features are generally moving away from Mexico and will pose no threat to land except for some minor increased wave activity in western Mexico, according to DaSilva.

On Saturday evening local time, a tropical storm in the East Pacific Ocean strengthened into Hurricane Hilda. As of early Sunday morning, Hilda was a Category 1 hurricane on the Saffir-Simpson Hurricane Wind Scale, located about 860 miles southwest of the southern tip of Baja California. The hurricane was packing sustained winds of 85 mph, moving to the west-northwest at 10 mph.

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Hilda is gradually gaining strength, according to AccuWeather Senior Meteorologist Adam Douty. However, as Hilda continues to move to the northwest, the storm will encounter drier air, stronger wind shear and cooler ocean water.

Hurricanes thrive in moist, warm environments, so each of these will work to degrade Hilda's wind intensity, which could cause it to become a tropical storm again. While Hilda is not anticipated to impact land, shipping interests should be aware of higher seas from the hurricane.

A tropical depression located to the west of Hilda became Tropical Rainstorm 9-E early Sunday morning, local time, about 1,405 miles west-southwest of Baja California and is remaining nearly stationary.

"Due to the lack of organization and convection associated with 9-E, the system has been classified as post tropical," said Douty. Though it was poorly organized on Sunday morning, there is a possibility of the rainstorm becoming a tropical depression again or even a tropical storm before moving into cooler waters. The next name on the list in the Pacific basin would be Ignacio.

There is also an area of low pressure on the opposite side of Hilda, which is forecast to develop into a tropical depression or even a tropical storm, battling Tropical Rainstorm 9-E to be the next named storm.

"There looks to be a small window for tropical development through about Monday," said Douty. Then, it is possible the low pressure will get close to Hilda, which can inhibit strengthening or even lead to weakening.

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This area of low pressure is anticipated to interact with Hilda and could get "sucked in" by the hurricane sometime next week, according to DaSilva. This would occur in a process called the Fujiwhara Effect.

The Fujiwhara Effect happens when two tropical systems spinning in the same direction pass close enough to each other that they begin to "dance" around a common center, according to the National Weather Service. Oftentimes, the two systems can approach each other and merge.

This phenomenon occurred earlier this year off the coast of Western Australia, when two systems, known as Seroja and Odette interacted.


"Seroja was the dominant feature, with the system formally known as Tropical Low Odette rotating in the clockwise fashion around Seroja," AccuWeather Meteorologist Mary Gilbert said in April.

Seroja absorbed what was left of Odette in a Fujiwhara dance. Now, such an event could happen in the East Pacific basin.

"While it is possible there is a Fujiwhara interaction between the storms, I think it is too early to say this with much confidence that this specific type of interaction will happen," said Douty.

Elsewhere, another developing storm could make waves in the Pacific later this week.

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This satellite image, taken early Sunday morning, local time, shows Tropical Rainstorm 9-E, Hilda and the low pressure area from left to right in the East Pacific. (RAMMB/CIRA)

"Models are hinting that another storm could develop west of Mexico late in the week or next weekend," said DaSilva. This storm has the potential to become a hurricane as well, though it is also expected to stay far off the coast, bringing few, if any impacts to Mexico.

Meanwhile, Hilda or Tropical Rainstorm 9-E could bring an increase in moisture to Hawaii around Aug. 8 through Aug. 10, but cooler waters and wind shear mean the systems should dissipate around then, according to Douty.

While the Pacific buzzes with activity, the Atlantic Ocean remains quiet, but not for long, according to DaSilva. The middle of the month, however, is looking to be a more active period for the Atlantic basin, and the peak of the season doesn't arrive until September, so there is plenty of time for the tropics to heat up.

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