Category ‘6’ tropical cyclone hot spots are growing

Climate change is making massive hurricanes and typhoons more likely in the western Pacific, North Atlantic and Gulf

American Geophysical Union

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NEW ORLEANS — The oceanic conditions that churn up the very strongest of hurricanes and typhoons are heating up in the North Atlantic and Western Pacific, fueled by warm water that extends well below the surface. Human-caused climate change may be responsible for up to 70% of the growth of storm-brewing hotspots there, according to new research.  

These hot spots are making it more likely that stronger Category ‘6’ tropical cyclones may hit landfall in highly populated areas.  

“The hot spot regions have expanded,” said I-I Lin, a chair professor in the Department of Atmospheric Science at the National Taiwan University. 

Lin will present the findings during an oral session on tropical cyclones at AGU’s 2025 Annual Meeting in New Orleans, Louisiana, on Wednesday, 17 December. From 15-19 December, AGU25 brings together more than 20,000 scientists to discuss the latest in Earth and space science research. 

Lin has been interested in the strongest hurricanes and typhoons for more than a decade. Typhoon Haiyan—also known as Super Typhoon Yolanda—struck the Philippines at maximum intensity in November 2013, killing thousands of people. The next year, Lin and her colleagues published a paper calling for the need for creating a new category of tropical cyclones—6—for the very strongest storms like Haiyan, in the AGU journal Geophysical Research Letters.  

Category 6 tropical cyclones would include those that exceed a wind intensity of 160 knots, Lin and her colleagues argue. Previously, any storm with winds above 137 knots were considered Category 5—most official weather agencies still recognize Category 5 tropical cyclones as the strongest. But since most other categories include a window of about 20 knots, Lin said it makes sense to create a Category 6. Category 4, for example, includes storms with wind intensity of 114-137 knots.  

Some of the best-known of these storms include Hurricane Wilma in 2005, the most intense hurricane recorded in the Atlantic basin, Typhoon Haiyan and Typhoon Hagibis, which struck Tokyo in 2019. The latter was among the costliest in terms of destruction from rain and wind, Lin said, even though it had downgraded in intensity by the time it hit the Japanese capital. Finally, Hurricane Patricia, which formed in the Pacific Ocean off the coast of Mexico, was the strongest tropical cyclone ever recorded, with wind intensity of up to 185 knots—enough to make it considered a Category 7 storm, if such a thing existed, Lin said. “Patricia was the king of the world,” she added.  

Burgeoning ocean hotspots feed big storms 

Lin and her colleagues looked back at all large storms recorded in the past four decades or so, and found that these Category ‘6’ storms are increasingly common. In three decades from 1982 to 2011, there were eight tropical cyclones that had wind intensity of more than 160 knots. In the more recent decade she examined, from 2013 to 2023, there were 10 Category 6 tropical cyclones. So, of 18 Category ‘6’ cyclones that occurred the past 40 years or so, 10 of them happened in the last decade.  

Lin’s ongoing recent work, the topic of her discussion at the upcoming session in the American Geophysical Union’s 2025 Annual Meeting, reveals that most of these Category ‘6’ tropical cyclones occur in hot spots. The largest hot spot for these massive storms is in the Western Pacific east of the Philippines and Borneo, while another hot spot lies in the North Atlantic around and to the east of Cuba, Hispaniola and Florida.  

Their work also reveals that these hot spots are growing in size—the North Atlantic hot spot has expanded eastwards past the northern coast of South America and westwards into much of the Gulf, while the Western Pacific has grown as well.  

The conditions that drive Category ‘6’ storms are driven by warmer subsurface water as well as warm surface water. In other regions, big storms often churn up the ocean. As cool water is drawn into the surface, it can cool the storm itself, reducing its intensity. But since warm water is so deep in these hot spot regions, the cyclones don’t have a chance to cool as much. Just the same, Lin cautions that not every storm that arises in these hot spots will become a Category ‘6’ tropical cyclone—the atmospheric conditions have to be right as well. “The hot spots are a necessary but not sufficient condition,” she said. 

Analysis of the factors driving this expansion of deeper warm water in these hot spots has revealed that global warming and natural variability in temperature both play a role. But overall, the team estimates that human-caused climate change is responsible for about 60-70% of the increased size in these hot spots—and consequently, of Category ‘6’ tropical cyclones.  

Lin said that recognition of Category ‘6’ tropical cyclones by weather agencies could help cities plan more appropriately for the impact of coming storms—especially in hot spot areas where they are becoming more common. “We really think there is a need just to provide the public with more important information,” Lin said.  

Contributed by Joshua Rapp Learn 

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Abstract information: 

A31A-06 Category ‘6’ Tropical Cyclone Hot Spots in the Warming Climate 
Wednesday, 17 December, 9:34 – 9:45 Central Time 
Room 278-279 (NOLA Convention Center) 

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AGU (www.agu.org) is a global community supporting more than half a million professionals and advocates in Earth and space sciences. Through broad and inclusive partnerships, AGU aims to advance discovery and solution science that accelerate knowledge and create solutions that are ethical, unbiased and respectful of communities and their values. Our programs include serving as a scholarly publisher, convening virtual and in-person events and providing career support. We live our values in everything we do, such as our net zero energy renovated building in Washington, D.C. and our Ethics and Equity Center, which fosters a diverse and inclusive geoscience community to ensure responsible conduct. 

Sri Lanka plans $1.6 bn in cyclone recovery

spending in 2026

Colombo (AFP) – Sri Lanka's government announced plans on Thursday for $1.6 billion in extra spending in 2026 to fund the country's recovery from Cyclone Ditwah, which killed more than 640 people.


Issued on: 18/12/2025 - RFI

The natural disaster affected 2.3 million people, more than 10 percent of Sri Lanka's population, and floods and landslides caused by the cyclone left extensive damage throughout the country.

The government convened parliament on Thursday, interrupting a month-long recess, to discuss what President Anura Kumara Dissanayake has described as the most challenging natural disaster to hit the island.

Dissanayake presented a request for an additional 500 billion rupees ($1.66 billion) for rebuilding devastated homes, roads, bridges and railways, as well as for cash handouts to help people regain lost livelihoods.

"We need to allocate an additional 500 billion rupees for disaster relief and reconstruction over and above the money allocated for government spending in calendar 2026," Dissanayake told parliament.

The national assembly, where his party holds a more than two-thirds majority, is expected to approve the mini-budget on Friday.

However, Dissanayake said the government does not intend to raise its borrowing limit to meet the additional expenditure.

He previously said he was banking heavily on foreign grants, and the finance ministry on Wednesday announced that it would call an international donor conference early next month.

The government has already asked the International Monetary Fund (IMF) for $200 million from a rapid relief fund and has secured World Bank agreement to repurpose $120 million from an ongoing project for disaster recovery spending.

On Tuesday, Sri Lanka also secured a $200 million loan from the Asian Development Bank to finance water management, the first such funding since the cyclone.

The finance ministry said the funds would be used to complete a canal network in the North-Central Province (NCP), which was among the worst affected by flooding last month.

"The objective of the project is to enhance agricultural productivity, farmer incomes and climate resilience in the NCP," the ministry said in a statement.

The World Bank has said it is in the process of assessing the damage caused by the cyclone, while Colombo has said preliminary estimates suggest it may need up to $7 billion to rebuild.

The cyclone struck as the country was emerging from its worst ever economic meltdown in 2022, when it ran out of foreign exchange reserves to pay for essential imports such as food, fuel and medicines.

Following a $2.9 billion bailout from the IMF approved in early 2023, the country's economy has stabilised.

© 2025 AFP

 

UF dives deep into predicting storm damage with computer models

University of Florida

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Though the 2025 hurricane season was relatively quiet for the United States, researchers are combining massive amounts of observational data with wildly complex computer models to predict the impact of future storms on coastal communities.  

The University of Florida’s Engineering School of Sustainable Infrastructure & Environment, or ESSIE, is part of a project that recently received the Excellence in Partnering Award by the National Oceanographic Partnership Program for its collaborative, multi-institutional effort aimed at improving prediction of coastal storm impacts. ESSIE’s team focused on creating models to predict such complex storm effects as breaching, erosion, water levels and property damage.  

Researchers hope the project will improve the accuracy of the models and enable residents and emergency managers to target specific risks and make storm preparations more effective and timelier. 

A key element of the project was testing models for accuracy, comparing predicted outcomes created with their models with actual outcomes. They used pre- and post-storm data from six hurricanes to test their models and predictions.  

Consisting of nine teams, each with a lead principal investigator, researchers on the project represented 13 unique academic institutions, 13 government agencies or divisions, and 11 industry performers.  

The Excellence in Partnering Award is given annually to a National Oceanographic Partnership Program project that best exemplifies the program’s objective of developing a successful network of partnerships to advance ocean sciences.  

Maitane Olabarrieta, Ph.D., professor in the UF Department of Civil & Coastal Engineering, was one of nine lead principal investigators on the project. She led the Waves, Sediment, Surge and Structure Response Forecasting System team. She is working alongside Arthriya Subgranon, Ph.D., a former assistant professor at the Herbert Wertheim College of Engineering. 

The massive project spanned four years and wrapped up in April. While Floridians are accustomed to predictions of a storm’s path and associated surge, researchers wanted to take hurricane prediction to the next level, providing reliable and useful predictions of storm effects that really matter — infrastructure and housing damage, erosion and accretion (the accumulation of sediment or matter). Olabarrieta said these real-world effects are notoriously hard to predict.  

So, how did the teams expand the scale of their predictions?  

Data. 

So much data.  

As part of the research, nine teams would spring into action each time a storm threatened to make landfall in Florida. The teams worked across a diverse set of modalities: atmospheric forecasting, high-resolution digital elevation mapping, remote sensing using synthetic aperture radar, drifting wave buoy deployment, nearshore sensor deployment and oceanic forecasting.  

As part of the oceanic forecasting effort, Olabarrieta’s team created models designed to predict coastal erosion and damage to infrastructure, combining data collected across all the teams and applying machine learning models — trained on masses of historical hurricane data — to ultimately create the prediction. 

One innovation was the inclusion of data gleaned from public sources.  

Subgranon and her doctoral student, Steven Klepac, mined data from local building permit offices for information about documented damage from previous storms. Building permits (applied for in rebuilding efforts) typically include information such as first-floor elevation, roof and wall materials and even neighborhood density. Their machine learning model, dubbed BuildForce, was trained on this historical data and ultimately fed information into the forecasting model.  

The combination of such varied and granular data with powerful prediction models, all running on UF’s HiPerGator supercomputer, enabled researchers for the first time to begin to predict specific storm effects such as water levels, building damage and coastal morphology changes.  

Leveraging the reams of data researchers had already collected, the pre- and post-storm comparisons revealed three of their models performed strongly in predicting storm waves, water levels, breaching, erosion and damage during recent hurricanes. 

As the goal is collaboration and improving predictions, all project data are publicly available on DesignSafe, a data repository funded by the National Science Foundation. The hope is that releasing the data to researchers worldwide will invite further collaboration and continued model improvements. 

To date, the effort has produced more than 10 scientific papers and over 50 conference/seminar presentations, underscoring its visibility and leadership in coastal resilience research. 

Researchers also collaborated with government agencies to create an engaging map to visualize the data and methods for the project. View it here.  

Olabarrieta sees this work as nothing short of transformative.  

“In an era of accelerating climate change, rising sea levels and increasing storm intensity, improving coastal impact prediction is an urgent societal need,” she said. “This project highlights the power of large-scale, collaborative science to meet that challenge. We are deeply thankful to our sponsors and collaborators for their exceptional partnership and for making this transformative project possible.” 

 

Study finds ocean sediments are key to survival of northeastern US salt marshes

UMass Amherst and Massachusetts Geological Survey researcher calls work a “wake-up call” about the critical role oceans play in helping marshes keep pace with rising seas

University of Massachusetts Amherst

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image: 

Wenxiu Teng (left), Brian Yellen (center), and Qian Yu (right) sample salt marsh sediments at East River Marsh in Guilford, Connecticut.

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Credit: UMass Amherst

UMass Amherst and Massachusetts Geological Survey researcher calls work a “wake-up call” about the critical role oceans play in helping marshes keep pace with rising seas

 

AMHERST, Mass. — Salt marshes, those critical habitats that protect coastal towns from flooding, store massive amounts of blue carbon, support fisheries and play a key role in ecological resilience, are struggling to survive as oceans rise due to climate change. A new study led by the University of Massachusetts Amherst and the Massachusetts Geological Survey reveals a previously undiscovered source of the sediments that are key to the salt marshes’ survival: the ocean. The research, published recently in Geophysical Research Letters, relies on an innovative method of working with satellite data to see a process that has been hitherto invisible and holds immediate implications for coastal management.

Salt marshes can only survive if they gain enough elevation to keep up with sea-level rise—which requires a steady supply of sediment. “Traditionally, scientists have assumed that most of the sediments for salt marshes came from rivers,” says paper coauthor Brian Yellen, Massachusetts State Geologist and UMass Amherst faculty member. “That assumption makes a lot of sense, but members of our team have previously shown that there’s not enough sediment in the rivers to keep marshes viable.”

What Yellen describes as a “wake-up call” for the scientific community pushed researchers to look at the other possible source of sediment—the ocean. But it’s very difficult to get a sense of how much sediment the ocean is flushing into salt marshes.

“You can deploy a sensor in the middle of a stream and get an accurate sense of how much sediment is flowing past it,” says Wenxiu Teng, lead author of the paper and a postdoctoral researcher at UMass Amherst. But along the coast, sediment is moved by waves, tides and storms across a wide, shifting area, making it nearly impossible to maintain enough instruments to measure those changes directly.

So Teng, Yellen and their colleagues looked skyward for inspiration.

For 40 years, the LANDSAT Earth-observing satellite system has been taking fairly high-resolution images of the entire planet and sending them back to us. Teng and his primary advisor, UMass Amherst Professor of Earth, Geographic, and Climate Sciences Qian Yu, have developed a sophisticated dataset that uses LANDSAT observations to make highly accurate estimates of ocean sediments, and with it, he and his co-authors looked at 103 salt marshes across the Northeast, from New York City to the Canadian border.

Not only were they able to confirm that the ocean is a significant source of sediment for much of the region’s salt marshes, they also found a clear north-south divide among those marshes that were getting enough sediment to keep up with sea level rise, and those that were drowning.

Marshes within Cape Cod Bay and into northern New England are generally doing well. But marshes in southern New England are showing signs of stress.

Using historical satellite imagery showed that Southern New England coastal sediment supply has been declining year over year since 2000, and the team hypothesizes that this dwindling supply could be due to coastal management that removes sediment from the coast. Sea walls and other armoring structures prevent bluffs from crumbling onto the beach to nourish coastal sediment. Dredging mud and disposing it offshore also starves the coastal ocean of sediment. In addition, wave energy in the region has been gradually weakening, reducing the ability of waves to stir up and transport sediment that would otherwise help sustain the salt marshes.

The authors warn that if this downward trend in sediment continues, many southern New England marshes may not be able to keep pace with rising seas. They recommend that coastal planners consider sediment impacts when designing restoration, dredging or shoreline protection projects. Notably, the authors developed a web-based application called SedXplorer that allows coastal managers to view satellite-derived suspended sediment dynamics themselves anywhere on earth.

“Coastal scientists have been debating whether salt marshes really need sediment,” says Teng. “This study adds one more piece of evidence that sediment is really important, and that a lot comes from the ocean in this region where rivers tend to run clear.”

“It also shows what a precious resource sediment is for maintaining coastal resilience in New England,” adds Yellen.

This study was supported by the Northeast Climate Adaptation Science Center (NECASC), part of the U.S. Geological Survey.

 

Contacts: Brian Yellen, byellen@umass.edu

                 Daegan Miller, drmiller@umass.edu

 

About the University of Massachusetts Amherst 

The flagship of the commonwealth, the University of Massachusetts Amherst is a nationally ranked public land-grant research university that seeks to expand educational access, fuel innovation and creativity and share and use its knowledge for the common good. Founded in 1863, UMass Amherst sits on nearly 1,450-acres in scenic Western Massachusetts and boasts state-of-the-art facilities for teaching, research, scholarship and creative activity. The institution advances a diverse, equitable, and inclusive community where everyone feels connected and valued—and thrives, and offers a full range of undergraduate, graduate and professional degrees across 10 schools and colleges and 100 undergraduate majors.  

  

Landsat 8 image acquired on November 17, 2018, showing clear river discharge mixing with turbid, sediment-rich coastal waters, displayed in true color.

Credit

NASA/UMass Amherst

Journal

Geophysical Research Letters

DOI

10.1029/2025GL118706 

Article Title

Marine-Sourced Sediment Supply Supports Salt Marsh Resilience to Sea Level Rise in the Northeastern US

Article Publication Date

16-Dec-2025