How forecasters watch Hurricane Dorian


Hurricane Dorian's race in the Atlantic, off the coast of Florida to the United States, is closely monitored by US weather services, who are trying to predict where it will hit the ground with more and more forecasting tools powerful.

The priority is to collect the most information about the hurricane itself, which is done mainly by sending planes in the storm, in rough missions commanded by specialized pilots.

On Friday, for example, seven aircraft flights from the Federal Oceanic and Atmospheric Agency (NOAA) and the Air Force, known as "hurricane hunters", were planned in and around Dorian.

They record temperature, humidity, atmospheric pressure, speed of sales and drop probes that take measurements up to the surface of the ocean. Buoys and weather balloons can also be scattered before and during the hurricane.

These "field" data are supplemented by data from even higher up: satellites from the meteorological services and NASA.

The US Space Agency has many satellites oriented towards the Earth. One of them, Suomi NPP, has his instruments focused on Dorian and gives information on its structure and strength, the temperature at the top of the clouds and the volumes of precipitation.

These gigabytes of data – from aircraft and satellites – are then made available to all global weather services, and feed the famous weather forecast models. There are hundreds of them.

The European model, developed by the European Center for Medium-Range Weather Forecasts, is recognized as the most accurate.

In Miami, a team of ten forecasters from the National Hurricane Center (NHC) produces, every three hours, a detailed forecast of the trajectory and intensity of storms in the Atlantic. At any given time, at least two forecasters are on duty, on eight-hour rotations.

These forecasters use the many global weather patterns and then produce their own prediction from what the different models indicate.

"You have to know what's going on around the world to make a forecast," says meteorologist Sim Aberson of Hurricane Research Center, because what happens in the Atlantic depends on the weather elsewhere.

For the trajectory, which is the number one priority for forecasters, forecasts have improved significantly since the 1970s.

The accuracy of the three-day US center announcements is currently 100 nautical miles (185 km), which was 24-hour precision in 1993. Last year, at 24 hours, the accuracy was less than 100 km, according to data published on the NOAA website.

In contrast, for hurricane intensity, models made less progress. Hurricanes are classified into five categories, mainly according to wind speed.

On average, the error, at three days, was about a category of difference, says Sim Aberson, about 25 km / h. "It's very difficult to accurately measure the strength of a hurricane."

It is for this reason that the service publishes probabilities (for example, 55% risk that West Palm Beach will be hit by winds exceeding 118 km / h), and a cone illustrating the possible course of the storm.

The animations seen on the television channels come directly from the forecasts of this team of 10 specialists in Miami.

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