When a tropical system appears on the horizon, some of us rush to the computer, call up the models and try to figure out where it might go, how strong it might get.
No matter that those models frequently resemble spaghetti, going in different directions. We want to know if a threat is looming, even before the National Hurricane Center does.
For these amateur forecasters – and those who want to be – here's more about models:
Where do you find models?
Several weather sites offer them. Just Google "hurricane forecast models." Weather Underground, at wunderground.com, displays the best performing models and attaches a link to see them for each specific storm.
What's with all those colorful lines?
Each line represents a model's best estimate of where a storm might go, generally up to seven days.
Models are often off target with weak disturbances because they need to see a closed circulation, like those in tropical storms and hurricanes, to provide a good starting point for the forecast. That's why early model runs usually are widespread, indicating a lot of uncertainty. When the models are in agreement, they'll be tight together.
How do models work?
There are two basic kinds.
Dynamical models analyze atmospheric information, such as winds, barometric pressure and temperatures, through mathematic equations. They tend to be the best performing models.
Statistical models draw on historical information, such as how past hurricanes reacted to the atmosphere. They can spit out a forecast fast, some within seconds.
How does the hurricane center use models?
Forecasters take the average of the best-performing models to help develop a projected path. They also factor in multiple runs by the same model, or what's called an ensemble.
The hurricane center posts accuracy records with track forecasts almost every year, the result of increasingly more sophisticated models.
Why doesn't the hurricane center display models on its site?
If people misread the models and get conflicting information, they might delay making important decisions, said James Franklin, the center's top hurricane specialist.
"Most folks out there don't know the difference between good and bad models," he said. "With our experience and expertise, we try to put out the best forecast we can. That's what we really want people to focus on."
What are the best models?
The ECMWF, GFDL, GFS, and UKMET have become increasingly accurate at predicting storm tracks, thanks to powerful supercomputers. The HWRF model also made strides in predicting intensity, an area where the hurricane center has struggled for decades.
For a complete list of models, and what all those acronyms stand for, visit http://www.nhc.noaa.gov/modelsummary.shtml.