Hurricane Irma track: Which forecast model should you trust?

WASHINGTON — Hurricane Irma, with its record strong winds, is lashing the Caribbean, but where will it go from there? 

Forecasters turn to computer simulations to try to predict a storm’s path and how strong it will be. 

Different computer models — often run by different governments and various agencies — use different recipes or formulas to mimic the atmosphere. They all also approximate current conditions differently. 

So the resulting models look like a plate of spaghetti thrown on a map. But in that messy mass, meteorologists can get an increasingly strong idea of where a storm like Irma is heading. 

A look at how those predictions are made: 

Who to trust

The place to start is the National Hurricane Center’s official forecast, say several meteorologists who are not part of the federal government. “You can’t beat the hurricane center forecast,” said Miami television meteorologist Max Mayfield, who was the director of the hurricane center from 2000 to 2007. 

The “forecast cone” for Hurricane Irma from the National Hurricane Center as of 11 a.m. ET, Wednesday, Sept. 6, 2017.

National Hurricane Center

The hurricane center sees computer models other people don’t, judges individual models and uses a consensus of the better performing models, he said. The center also shows how well they do over time — and they are doing better. The trouble, say those experts, is that those same images of models are spreading over social media and they are getting misread. There are even bogus hurricane tracks spreading on social media. 

How good are the predictions?

Forecasters track the beginnings of storms, whether they come out of unstable weather that pops up in the Gulf of Mexico, or chug off Africa in classic Atlantic storm mode like Irma. The models usually agree about where the storm will go for the next 12 to 24 hours and then spread out with time. 

Today, the five-day forecast is as good as the three-day forecast was 15 years ago. And the margin of error for the five-day track forecast is nearly half of what it was when it was first introduced in 2001. What’s key is that meteorologists don’t stick to a single line or track because a slight change can mean a big difference, Mayfield said. For example, a tiny turn over Cuba, where mountains can eat up storms, can weaken Irma considerably. 

What goes into a model?

Computer models are like massive apps that try to solve complex…

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