Google DeepMind、気象モデル「WeatherNext」がサイクロンの経路と強度を同時予測

The model was built with the National Hurricane Center (NHC), the Cooperative Institute for Research in the Atmosphere, and the UK Met Office. Since June 2025, forecasts have been running live on Google's Weather Lab. During Hurricane Melissa, which made landfall in Jamaica in 2025, the model helped the NHC predict the storm's rapid intensification in time, according to Deepmind. That's when a storm gains at least 30 knots (about 34 mph) in wind speed within 24 hours.

WN-C solves a decades-old tradeoff

Cyclone forecasting has long suffered from a tradeoff. Global models like ECMWF's ensemble system (ENS) are strong on track prediction but too coarse for intensity. Specialized regional models like NOAA's Hurricane Analysis and Forecast System (HAFS) deliver more precise intensity readings but lose accuracy on the track. WN-C handles both in a single system, according to a paper published in Nature.

For a five-day forecast, the estimated storm center position is off by an average of 230 kilometers, compared to 370 kilometers for ENS and 335 kilometers for Deepmind's predecessor model GenCast. On three-day intensity forecasts, WN-C is 3.75 knots (about 4.3 mph) more accurate than HAFS.

WN-C also scores more than twice as well as ENS and GenCast on probabilistic storm intensity forecasts across many lead times. For the probability of 64-knot winds, the threshold where a storm reaches hurricane strength, the model delivers higher practical value for decision-making than ENS, according to Deepmind.

Coarse data, sharper forecasts

WN-C works with a data grid where each point covers about 28 kilometers, roughly a hundred times coarser than specialized regional models. Even a compact variant with 111 kilometers per grid point produces competitive results, Deepmind says.

"High resolution is not a strict prerequisite for state-of-the-art intensity forecasting," the authors write. The coarse weather data apparently contains more information about storm strength than anyone thought. How the models generate such accurate forecasts at this resolution remains an open research question.

Functional generative networks replace diffusion

WN-C uses Functional Generative Networks (FGN). GenCast relies on diffusion, a method best known from AI image generators, and needs dozens of passes through the neural network per forecast step. FGN gets by with a single pass, making it eight times faster.

To capture uncertainty, the system doesn't add noise to individual pixels the way most approaches do. Instead, it injects noise into the network's control layers. This produces different but physically consistent scenarios rather than just noisy variants of the same output.

Training on two very different data sources was key. The team used nearly 20 terabytes of global atmospheric data from ECMWF analyses along with a curated database of roughly 5,000 historical cyclones. To let the model learn from both sources together, the tabular storm data, including position, intensity, and extent, gets projected onto the same geographic grid as the weather data.

That lets the network predict track, intensity, and wind radii directly. Ablation studies in the paper show that this joint training is what drives the improvements.

1,000 scenarios per storm

A 15-day forecast runs in under a minute on one of Google's AI chips, so Deepmind scaled the number of parallel forecast runs from 50 to 1,000. Large ensembles like this could help capture rare extreme events more reliably. The Critical Success Index, which weighs correct warnings against false alarms and missed events, jumps from below 0.3 to 0.5, according to the paper.

A complement, not a replacement

Traditional numerical models still matter, according to Deepmind. The NHC typically combines results from several physics-based models into a weighted average for its official forecasts, split between track (TVCN) and intensity (IVCN). In a simulated weighted addition to these consensus models, WN-C improves track forecasts by an average of 28 percent. For intensity, the gain is about 6 percent. The smaller intensity improvement shows that traditional models still contribute heavily in that area.

A model years in the making

Deepmind has made all of this publicly available, releasing the code and weights for both WeatherNext 2 and WeatherNext Cyclones on GitHub. The mini variant runs on a single TPU in a free Colab notebook. For official warnings, the authors still point users to national weather services. WN-C is meant to support forecasters, not replace them.

Last year, Deepmind introduced WeatherNext 2, the underlying weather AI that is now open-source along with the cyclone variant. In June 2025, Deepmind and Google Research launched Weather Lab, a platform built for cyclone forecasting whose experimental model has now become WeatherNext Cyclones. The collaboration with NHC and CIRA was already in place at that point.

Before that, Deepmind released GenCast in late 2024, the first probabilistic weather model to beat ECMWF's ensemble, also open-source. WN-C swaps out GenCast's diffusion approach for the faster FGN method and broadens the scope to tropical cyclones.

Google's track record with forecasting hasn't always been this strong, though. Its Android Earthquake Alerts system severely underestimated the 2023 Turkey earthquakes, rating a 7.8 quake at just 4.5 to 4.9 and sending only 469 critical warnings when millions should have been alerted.

The scientific achievement comes during a turbulent stretch for Deepmind itself. CEO Demis Hassabis recently stepped back from day-to-day operations to become Alphabet's Chief Scientist, while chief researcher Jeff Dean left after 27 years to co-found the AI startup Discovery Loop with several other senior researchers.