NOAA Retires the NAM, the Forecast Model Known for Overhyping Florida Hurricanes, in Favor of the Rapid Refresh Forecast System

The National Oceanic and Atmospheric Administration has retired the North American Mesoscale Forecast System, the short range computer model better known to Florida weather watchers as the NAM, and replaced it with a new, faster updating system called the Rapid Refresh Forecast System. The NAM had a long reputation in Florida for showing hurricanes far stronger than they turned out to be and for struggling with the state's summer sea breeze thunderstorms.

National Weather Service service change notices set the switch for 1200 UTC on Tuesday, Nov. 3, 2026, which is 7 a.m. Eastern time. WUSF and the Florida Public Radio Emergency Network reported Thursday that the model has been shut down after roughly two decades in operation.

What NOAA shut off

The retirement goes well beyond a single model. In Service Change Notice 26-47, updated Oct. 2, the weather service said the National Centers for Environmental Prediction would discontinue the NAM, the Short Range Ensemble Forecast (SREF), the High Resolution Ensemble Forecast (HREF), the High Resolution Window (HiresW) and the NAM Model Output Statistics, a set of statistical forecast products built from NAM output. The notice said these "legacy systems are being replaced by the Rapid Refresh Forecast System (RRFS)."

The NAM products being shut off cover every domain the model ran, including the continental United States, North America, the Caribbean and Central America, Alaska, Hawaii and Puerto Rico. The HiresW will continue to run only for Guam.

The timing was not fixed in stone. Both notices said that if the implementation date were declared a Critical Weather Day, or if other significant weather was occurring or expected, the change would move to 1200 UTC on the next weekday free of such conditions. The start date had already shifted several times in earlier versions of the notices, from a target of Aug. 31 to dates in October before settling on Nov. 3. An Oct. 15 update to the RRFS notice kept the Nov. 3 date.

The NAM's rocky record in Florida

According to WUSF, the NAM had been running since about 2005 and produced forecasts up to 84 hours, or three and a half days, ahead. Meteorologists used it mainly for localized precipitation events, and forecasters said it filled gaps where larger global models fell short, particularly in winter weather setups.

In Florida, its reputation was more mixed. The model tended to overpredict events, especially during hurricane season, WUSF reported. It often showed a tropical cyclone's minimum central pressure far below what was actually observed. Because lower pressure signals a stronger storm, those runs implied a more intense hurricane than the one that arrived, and the outlet noted that being a category or two off makes a big difference in potential damage. The NAM was also frequently an outlier compared with other forecast systems.

The model performed well along the Appalachians and the Interstate 95 corridor, according to WUSF, but struggled in Florida with summer sea breeze thunderstorms and tropical events. Those afternoon storms, which form where the Atlantic and Gulf breezes collide over the peninsula, drive much of Florida's rainy season weather.

Audrey Shirley, a meteorologist with the Florida Public Radio Emergency Network, said she had relied on the model for years. "Using the NAM became part of my daily forecast routine, even though it over-exaggerated rainfall and cloud cover," she said. "So, it's more of a sentimental loss for me."

What replaces it

The Rapid Refresh Forecast System is built to update far more often than the NAM did. WUSF reported that the NAM ran about four times a day, while the RRFS produces output every hour and incorporates radar, observation and satellite data.

Service Change Notice 26-48 describes the new system in detail. The RRFS is "an hourly updated modeling system covering the North America region at 3 km horizontal grid spacing." Its four main daily runs, at 00, 06, 12 and 18 UTC, extend 84 hours, matching the NAM's range, while the other hourly runs go out 18 hours. It also produces output for Puerto Rico and Hawaii at 2.5 kilometer spacing, and a separate 1.5 kilometer run for fire weather.

A companion ensemble, the RRFS Ensemble Forecast System (REFS), replaces the HREF. It combines five RRFS ensemble members, which use different starting conditions and model physics to cover a range of possible outcomes, with the deterministic RRFS run and the High Resolution Rapid Refresh (HRRR) for the continental United States. The REFS produces products out to 60 hours, compared with 48 hours for the HREF, and includes flash flood and rainfall recurrence interval probabilities for the continental United States.

The weather service said the new system will "greatly unify and simplify" the suite of regional models that operate at roughly 3 kilometer spacing, the scale at which individual thunderstorms can be represented. Development was a joint effort of the weather service's Office of Modeling and Development and NOAA's Global Systems Laboratory, along with academic, federal and international partners. A real time parallel feed of the RRFS and REFS had been available to forecasters and the public since Aug. 12, 2026.

The HRRR, another hourly model many Florida forecasters watch closely on thunderstorm days, is not part of this retirement. It remains in operation and supplies members to the new ensemble.

Early adjustments to the new model

The new system has already been tuned during testing. The Oct. 15 update to the implementation notice said NOAA replaced the RRFS's microphysics based instantaneous precipitation type product with a diagnosed, thermodynamic based calculation and removed accumulations of freezing rain and sleet from the output. The notice said the changes responded to "an over-forecasting of freezing rain and under-forecasting of sleet" within the RRFS and REFS. That is mostly a concern for colder states, but it shows forecasters will still be learning the new model's habits.

Why it matters for Floridians

Most Floridians never looked at a NAM run directly, but the model's output reached them through television forecasts, apps and social media maps. Its tendency to deepen tropical systems produced dramatic graphics that circulated widely during hurricane season, sometimes showing what WUSF described as a record breaking hurricane that never materialized.

A model that refreshes every hour with fresh radar and satellite data is designed to capture fast changing, small scale weather better, the kind of setup that produces Florida's afternoon storms and localized flooding rain. NCEP said the move away from the NAM and several other short range products is part of a broader effort to modernize its operations and forecasting, WUSF reported.

The change arrived during an active week for Florida weather. The switch was scheduled for the same Tuesday that record rain was flooding Brevard County, the Treasure Coast and parts of South Florida.

What's next

With the NAM gone, forecasters across Florida will lean on the RRFS and REFS for short range guidance, alongside the HRRR and the global models. Its real test in the state will come next summer, during the sea breeze season, and during the 2027 Atlantic hurricane season, which begins June 1. Users can send questions about the new system to the weather service's Office of Modeling and Development, according to the service change notices posted at weather.gov/notification.