HONOLULU (HawaiiNewsNow) - Over the summer, several rounds of record-breaking high tides swallowed up stretches of Hawaii beaches and put flood-prone areas like Mapunapuna virtually underwater.
What started off as an anomaly became almost routine after these "king tides" started arriving in waves — coming in on what seemed like a monthly basis.
So why were these king tides so prevalent only this year?
Scientists point to a few key factors -- such as normal seasonal high tides, a type of ocean circulation, a large swell event and long-term sea level rise -- all stacked up on each other.
But perhaps the most elusive of them all: The "blob," an area of warmer and higher seas concentrated around the Hawaiian island chain.
"It has hung around so long that we have named it … 'Nu'a Kai,' a build-up of the sea," said Chip Fletcher, associate dean and professor of geology and geophysics at the University of Hawaii's School of Ocean and Earth Science and Technology.
Not a lot of information exists as to what caused the "Nu'a Kai," which has persisted all year. But scientists all agree that it's somehow related to the strong El Niño years of 2015 and 2016.
"Unusual for Honolulu is that sea levels have been above normal every month since the end of the strong El Niño in 2016," said Matthew Widlansky, a sea level researcher for the University of Hawaii's Joint Institute for Marine and Atmospheric Research program.
El Niño — a natural recurring warming in the equatorial Pacific Ocean that influences air and moisture movement around the globe — can be blamed for a record-breaking number of tropical cyclones in the Pacific in 2015 along with a mass global coral bleaching event, among many other phenomenon.
This is not the first time something like this has baffled scientists. In 2013, scientists detected a similar blob – which covered roughly 3.5 million square miles – from Mexico to Alaska. It persisted all the way to 2015.
Research found that the blob resulted in increased ozone levels above the western U.S., impacting the air quality. The "vast, warm patch" was also linked to mass die-offs in the ocean and toxic algal bloom along the west coast.
Widlansky said researchers are still actively looking at persistent high sea levels and whether similar events can be forecast in advance.
"One question, in particular, is why haven't similar prolonged high sea level events occurred here in years past like after the previous strong El Niño that ended in 1998?"
But in general, king tides — an Australian term used to define a very high tide that could lead to flooding in a coastal community — are a result of several factors. Those include the fact that tides are normally at their highest at this time of year because of the Earth's proximity to the moon; a type of ocean circulation (or what scientists call a mesoscale eddy); a large swell event; and long-term sea level rise that creates a rising background effect.
While it's still not understood how this "blob," or persistent high sea levels, is linked to climate change, scientists say climate change could lead to more and stronger El Niños.
And what comes along with persistent high sea level events: Major coastal impacts like beach erosion and coastal flooding.
"What is well understood is that ongoing global sea level rise caused by warming oceans and melting land ice will continue to exasperate coastal impacts during high sea level events like what we have experienced this summer in Hawaii," Widlansky said.
The next king tide event is expected to occur in December.