But mariners often need to make binary decisions based on nebulous weather forecasts.

From Into the Raging Sea by Rachel Slade. Page 50.

Uncertainty in forecasting can be quantified. When models contradict one another, uncertainty is expressed as a probability.

In the course of everyday life, we don’t often encounter uncertainty. Gamblers and hedge funders may weigh odds all day, but most of us aren’t sure what to do if someone says she’s 30 percent sure she’s wrong. How do you process that, especially in a world where so many decisions are made for us by technology?
“If the definition of wisdom is understanding the depths of your own ignorance, meteorologists are wise,” says Kerry Emanuel, an MIT professor who has dedicated his life to understanding weather and climate. “It’s wise but it’s a wisdom that is not recognized. If you say there’s a lot of uncertainty in this, in the modern world, it’s translated as You don’t know anything.”

Due to uncertainty, prudent mariners follow the 3-2-1 rule: Three days ahead of a hurricane’s forecasted position, stay three hundred miles away; two days ahead, keep out of a two-hundred-mile radius of its projected center; one day ahead, stay one hundred miles away from its eye in all directions. The rule is based on the fact that hurricane paths are erratic and unpredictable, so it’s smart to give the system a wide berth.

But mariners often need to make binary decisions based on nebulous weather forecasts. On October 24, 1998, the elegant Fantome, a 679-ton staysail schooner built in 1927, departed Honduras for a six-day Windjammer cruise. A thousand miles away, Hurricane Mitch rumbled in the Caribbean Sea. As Mitch picked up strength, the captain of the Fantome got nervous and discharged his passengers in Belize City, then headed north toward the Gulf of Mexico to outrun the storm.

Forecasting Mitch proved extremely difficult due to weak steering winds, but the official NHC prediction, issued with multiple caveats, was that the storm would go north toward Mexico’s Yucatan Peninsula. When the Fantome’s captain received that forecast, he hove to and headed south, unwittingly right into the hurricane’s path, which, contrary to forecasts, took a left turn toward Central America. On October 27, fighting hundred-mile-per-hour winds and forty-foot seas, the Fantome was lost forty miles south of the hurricane’s deadly eye wall.

Well put. Not just mariners. All of us often need to make binary decisions based on uncertain forecasts.

We have to lock into a specific and usually unchangeable course of action even though we know the exogenous circumstances are likely to change.