Predicting Irma's path is giving supercomputers a challenge

When it comes to hurricane prediction, the consensus is on the need for consensus among forecasters. No single computer model should be relied on. And no forecast remains static.

So as Hurricane Irma roars through the Caribbean, forecasters are looking at the top weather models from Europe, the United States and Britain, collectively, to track what on Tuesday was already being described as the second-strongest storm observed in modern times.

But even the world’s best weather minds and most powerful computers can’t say precisely where the Category 5 storm is headed or whether it will retain its 185 mph winds when it hits the U.S., probably sometime this weekend. One major factor that can't yet be determined: whether Irma will hit Cuba and lose power along with the energy-sustaining warmth it gained over the open ocean.

28 PHOTOS
Preparing for Hurricane Irma
See Gallery
Preparing for Hurricane Irma
YEMASSEE, SC - SEPTEMBER 08: Northbound lanes of I-95 near the Georgia-South Carolina border are empty as northbound lanes are packed as pepole evacuate ahead of the arrival of Hurricane Irma September 8, 2017 in Yemassee, South Carolina. Florida appears to be in the path of the hurricane which may come ashore at category 4. (Photo by Chip Somodevilla/Getty Images)
ST. PETERSBURG, FL - SEPTEMBER 05: Stan Glass, of St. Petersburg, fills four 5-gallon fuel tanks with gasoline for his boat should he have to evacuate by boat as residents in the area prepare ahead of Hurricane Irma on September 05, 2017 in St. Petersburg, Florida. The National Hurricane Center (NHC) has reported that Hurricane Irma has strengthened to a Category 5 storm as it crosses into the Caribbean and is expected to move on towards Florida. (Photo by Brian Blanco/Getty Images)
A woman looks at empty shelves that are normally filled with bottles of water after Puerto Rico Governor Ricardo Rossello declared a state of emergency in preparation for Hurricane Irma, in San Juan, Puerto Rico September 4, 2017. REUTERS/Alvin Baez
People buy materials at a hardware store after Puerto Rico Governor Ricardo Rossello declared a state of emergency in preparation for Hurricane Irma, in Bayamon, Puerto Rico September 4, 2017. REUTERS/Alvin Baez
As Hurrcane Irma approaches Florida September 8, 2017 shoppers in Port St. John, near Kennedy Space Center, find almost empty shelves. Warning that Irma would be worse than Hurricane Andrew, which killed 65 people in 1992, Florida's governor said all of the state's 20.6 million inhabitants should be prepared to evacuate. / AFP PHOTO / BRUCE WEAVER (Photo credit should read BRUCE WEAVER/AFP/Getty Images)
People buy materials at a hardware store after Puerto Rico Governor Ricardo Rossello declared a state of emergency in preparation for Hurricane Irma, in Bayamon, Puerto Rico September 4, 2017. REUTERS/Alvin Baez
Workers put boats on dry docks in preparation, as Hurricane Irma, barreling towards the Caribbean and the southern United States, was upgraded to a Category 4 storm, in San Juan, Puerto Rico September 4, 2017. REUTERS/Alvin Baez
Customers walk near empty shelves that are normally filled with bottles of water after Puerto Rico Governor Ricardo Rossello declared a state of emergency in preparation for Hurricane Irma, in San Juan, Puerto Rico September 4, 2017. REUTERS/Alvin Baez
People buy materials at a hardware store after Puerto Rico Governor Ricardo Rossello declared a state of emergency in preparation for Hurricane Irma, in Bayamon, Puerto Rico September 4, 2017. REUTERS/Alvin Baez
People buy material at a hardware store after Puerto Rico Governor Ricardo Rossello declared a state of emergency in preparation for Hurricane Irma, in Bayamon, Puerto Rico September 4, 2017. REUTERS/Alvin Baez
Workers put boats on dry docks in preparation, as Hurricane Irma, barreling towards the Caribbean and the southern United States, was upgraded to a Category 4 storm, in San Juan, Puerto Rico September 4, 2017. REUTERS/Alvin Baez
Hurricane Irma, a record Category 5 storm, churns across the Atlantic Ocean on a collision course with Puerto Rico and the Virgin Islands, is shown in this NASA GOES satellite image taken at 1715 EDT (2215 GMT) on September 5, 2017. Courtesy NASA/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY
Members of the Civil Defense prepare their gear ahead of Hurricane Irma, in Santo Domingo, Dominican Republic September 5, 2017. REUTERS/Ricardo Rojas
A member of the Emergency Operations Committee (COE) monitors the trajectory of Hurricane Irma in Santo Domingo, Dominican Republic September 5, 2017. REUTERS/Ricardo Rojas
A member of the Emergency Operations Committee (COE) monitors the trajectory of Hurricane Irma in Santo Domingo, Dominican Republic September 5, 2017. REUTERS/Ricardo Rojas
Shoppers in a Home Depot store wait for plywood in the Little Havana neighborhood in Miami, Florida, September 5, 2017. Residents are preparing for the approach of Hurricane Irma. REUTERS/Joe Skipper
Men cover the windows of a auto parts store in preparation for Hurricane Irma, in San Juan, Puerto Rico September 5, 2017. REUTERS/Alvin Baez
A man uses a cable to secure the roof of his home in preparation for Hurricane Irma, in Toa Baja, Puerto Rico September 5, 2017. REUTERS/Alvin Baez
Men cover the window of a house in preparation for Hurricane Irma, in Toa Baja, Puerto Rico September 5, 2017. REUTERS/Alvin Baez
Empty boxes of produce at Costco as customers purchased all the product on September 5, 2017 in Miami. The monster hurricane coming on the heels of Harvey, which struck Texas and Louisiana late last month, is expected to hit a string of Caribbean islands including Guadeloupe late Tuesday before heading to Haiti and Florida. The Miami-based National Hurricane Center said Irma had strengthened to the most powerful Category Five, packing winds of 180 miles (280 kilometers) per hour. / AFP PHOTO / Michele Eve Sandberg (Photo credit should read MICHELE EVE SANDBERG/AFP/Getty Images)
Shoppers at Costco buying essentials in preparation for Hurricane Irma on September 5, 2017 in North Miami. The monster hurricane coming on the heels of Harvey, which struck Texas and Louisiana late last month, is expected to hit a string of Caribbean islands including Guadeloupe late Tuesday before heading to Haiti and Florida. The Miami-based National Hurricane Center said Irma had strengthened to the most powerful Category Five, packing winds of 180 miles (280 kilometers) per hour. / AFP PHOTO / Michele Eve Sandberg (Photo credit should read MICHELE EVE SANDBERG/AFP/Getty Images)
Costco ran out of water as people shop to prepare for Hurricane Irma on September 5, 2017 in North Miami. The monster hurricane coming on the heels of Harvey, which struck Texas and Louisiana late last month, is expected to hit a string of Caribbean islands including Guadeloupe late Tuesday before heading to Haiti and Florida. The Miami-based National Hurricane Center said Irma had strengthened to the most powerful Category Five, packing winds of 180 miles (280 kilometers) per hour. / AFP PHOTO / Michele Eve Sandberg (Photo credit should read MICHELE EVE SANDBERG/AFP/Getty Images)
Very long checkout lines at Costco as some people waited up to 8 hours to check in, shop and leave in preparation for Hurricane Irma on September 5, 2017 in North Miami. The monster hurricane coming on the heels of Harvey, which struck Texas and Louisiana late last month, is expected to hit a string of Caribbean islands including Guadeloupe late Tuesday before heading to Haiti and Florida. The Miami-based National Hurricane Center said Irma had strengthened to the most powerful Category Five, packing winds of 180 miles (280 kilometers) per hour. / AFP PHOTO / Michele Eve Sandberg (Photo credit should read MICHELE EVE SANDBERG/AFP/Getty Images)
A woman takes a photo of a boarded up business in advance of Hurricane Irma's expected arrival in Fort Lauderdale, Florida, U.S., September 8, 2017. REUTERS/Carlo Allegri
YEMASSEE, SC - SEPTEMBER 08: Northbound lanes of I-95 near the Georgia-South Carolina border are empty as northbound lanes are packed as pepole evacuate ahead of the arrival of Hurricane Irma September 8, 2017 in Yemassee, South Carolina. Florida appears to be in the path of the hurricane which may come ashore at category 4. (Photo by Chip Somodevilla/Getty Images)
As Hurrcane Irma approaches Florida September 8, 2017 residents of Titusville, near Kennedy Space Center, have arleady exhausted the lumber yards of plywood used to board up windows. Irma is expected to arrive in the area Sunday afternoon, September 10th. Warning that Irma would be worse than Hurricane Andrew, which killed 65 people in 1992, Florida's governor said all of the state's 20.6 million inhabitants should be prepared to evacuate. / AFP PHOTO / BRUCE WEAVER (Photo credit should read BRUCE WEAVER/AFP/Getty Images)
As Hurrcane Irma approaches Florida September 8, 2017 residents of Titusville, near Kennedy Space Center, have stop for last minute items and fuel. Gas prices had already been raised because of Hurricane Harvey hitting Texas, making gasoline cost more per gallon than diesel fuel. Warning that Irma would be worse than Hurricane Andrew, which killed 65 people in 1992, Florida's governor said all of the state's 20.6 million inhabitants should be prepared to evacuate. / AFP PHOTO / BRUCE WEAVER (Photo credit should read BRUCE WEAVER/AFP/Getty Images)
HIDE CAPTION
SHOW CAPTION
of
SEE ALL
BACK TO SLIDE

The best hurricane forecasting systems today are global models that solve the mathematical equations about the behavior of the atmosphere all over the world, said Jeff Masters, director of meteorology at the Weather Underground, a research group he founded.

Tops among half a dozen of these systems in recent years has been the ECMWF, the European Union’s super-computing system. The European Center for Medium-Range Weather Forecasting, known to those in the trade as the "European Model," has used very high-powered computers for more than a decade to model weather patterns around the globe.

The models, known as four-dimensional variational data assimilations (or 4D-Var) are expensive and take longer to assemble — producing two projections a day compared to the faster modeling systems run in the United States, which produce four or more projections every 24 hours.

The results from the private European system are available only to subscribers and are costly, but experts said they have been the most reliable in recent years.

“The idea behind their model is to forecast for the entire globe,” said Ryan Maue, a research meteorologist for WeatherBELL Analytics. "The theory is that, if they can get as much of the atmosphere around the globe correct as possible, then the tropical cyclones in the model will go in the right places and do the right things.”

Put another way, Maue said: “If you had to go in a casino and bet on one model, you would bet on the ECMWF, because it would be right more often than the others.”

But Maue and other experts stressed that they look at the European model along with many others in trying to predict the path and intensity of storms like Irma.

The principal predictive tool operated in the United States is the Global Forecasting System (GFS), run by the National Weather Service. Models generally have become twice as good in predicting storm tracks over the last two decades and the GFS system is particularly strong in this regard, said Masters.

The National Hurricane Center in Miami uses both the European and America’s GFS system, along with several other computer modeling systems to make its forecasts. Britain’s UKMET system is known for accuracy derived, like the European system, from high-powered 4D modeling. America’s HWRF (Hurricane Weather Research and Forecasting) uses real-time data, including from airplanes, to track ocean waves and, thereby, wind speeds.

Maue said HWRF did a “fantastic” job predicting the rapid intensification of Hurricane Harvey, as it prepared to make landfall last week. That remains one of the most difficult challenges for forecasters — because accurate intensity calls allow individuals, and governments, to decide when evacuations are a must.

The importance of perusing multiple models was exemplified again this week as the GFS model predicted a phenomenally low 870 millibar atmospheric pressure reading, said Masters. That would indicate winds of 200 miles per hour, or more, could be on the way.

But Masters said the European and HWRF models factor in the immediate impact of the winds in stirring up colder, sub-surface ocean water. That colder water will tend to decrease the power of the storm, increase pressures into the 920-millibar range, and reduce wind speeds. So while the GFS model might indicate “a ridiculous, totally off the scale, hurricane," Masters said, "the other models say it’s likely we merely have a ridiculous hurricane.”

As much as the science of hurricane prediction has improved, there is a lot left to know. Predictions made four days prior to landfall still end up being an average of about 175 miles off the mark, said Masters.

Related: How to Help Storm Victims

Even with all the models and improvements, experts still don’t know a couple of crucial things about Irma: How will local "steering currents" fluctuate, hour by hour, to redirect the storm as it gets closer to shore? What will be the exact location, and strength, of pressure systems around the U.S. that will determine when Irma turns northward?

The huge storm will look for the path of least resistance — probably toward a trough of low pressure to the north. That would cause Irma to make a right turn up into the Atlantic Ocean, said Maue, a popular scientist, whose weather charts are followed closely by other meteorologists.

“That means it most likely will not head into the Gulf [of Mexico] but will turn north,” said Maue, “Irma is going to hit a big brick wall; we are just not sure exactly when.”

Read Full Story