-- A UM ensemble model, used to create seasonal forecasts, accurately called for an increase in the number of major storms and a spike in storm energy for the season, which eventually produced 10 hurricanes in a row for the first time in more than a century.
-- A Princeton-based NOAA model and the Climate Prediction Center correctly produced Harvey's extreme rain days before the hurricane struck. Another experimental model that issues hourly forecasts for hazardous weather predicted the spot where Irma would make landfall 28 hours in advance.
All these improvements add up to better forecasts which, for emergency managers and the public, can mean better preparation. In flood-prone cities like New Orleans and Houston, or states like Florida that are wrapped by a coast vulnerable to storm surge, a month's warning about potential hazards could mean saved lives.
The advances also go beyond hurricane research. Kirtman's new monthly model, dubbed SubX, extends forecasts out to 34 days. Coupled with the ensemble model that predicts seasonal weather, it could allow meteorologists to make forecasts further into the future.
"Suppose you're planning a trip to Disney," he said. "I can't tell you definitively, but I can tell you there's a 20 percent chance the whole five days it's going to rain, or there's a 70 percent chance."
The models could also fill another critical gap: forecasting more imminent threats from climate change.
A warming planet that traps more moisture is expected to produce more intense hurricanes, but so far impacts like hurricanes and sea rise are generally forecast on global scales over years. Earlier this month, the U.S. government's National Climate Assessment warned more intense hurricanes with heavier rain will likely increase in the coming decades. Oceans, which have risen globally by 7 to 8 inches since 1900 and continue to rise faster than at any time in the last 2,800 years of records, could also trigger more extreme flooding, the report said.
But that's not the kind of information that could help ongoing work, like the $16 billion Everglades restoration project or a new voter-approved $400 million bond to address sea rise in the city of Miami. Impacts are not expected to rise along a straight line, but bobble up and down between wetter and drier and colder and warmer years, like a roller coaster that steadily rises. Predicting the bobbles will be critical.
"It's these shorter term fluctuations on top of the climate change signal where the real vulnerability kicks in," said Kirtman, director of the Cooperative Institute for Marine and Atmospheric Studies, a research partnership between 10 universities and NOAA.
"You have this chronic problem, but then all of a sudden you have an acute problem on top of that chronic problem and that makes it catastrophic. It's these risk multipliers and hazard multipliers and the interaction of timescales and that's where we're really trying to help."