AI
Friday, September 10, 2004 11:07:37 AM
*** Where will Ivan go? ***
Appears all the models have it going to FL.
===============================================================
Hi SM,
Thankfully, not all of them are in agreement. Some of the models start to diverge after exiting Jamaica.
If you're interested, the following article presents a good explanation of why that is happening....
Where will Ivan go?
By JAMIE THOMPSON
Published September 10, 2004
Millions of Floridians reeling from two hurricanes are anxiously awaiting the answer to one simple question:
Is Ivan coming here?
The best estimate of the National Hurricane Center in Miami is based on a half-dozen computer models that analyze millions of pieces of data from England to California.
But even with the aid of technical measurements such as wind radii and stepped microwave radiometer data, hurricane prediction still involves some educated guesswork.
Some models say Tampa Bay may be in danger. Others point to the east coast. Still others spiral it away from the U.S.
While it's always difficult to plot a hurricane's path more than three days out, Ivan is particularly confounding to the models.
"I think there's more disagreement with Ivan," said Ernie Jillson, meteorologist with the National Weather Service in Ruskin. "After Ivan passes Jamaica, the models spread out - some off into the Gulf of Mexico, others east near the Bahamas."
In the past three days, the forecast tracks for Ivan have zigzagged across the state. With every shift, fear ripples through communities on all sides of the skinny lines.
"There's always a certain amount of disagreement in any storm, when you get out in the four, five day time frame," said Robert Molleda, meteorologist with the hurricane center. "For Frances, the models seemed to be in a little better agreement over farther time frames. But with Ivan, we're still seeing divergence."
The reason, experts say, are variables in the atmosphere. Sometimes it has distinct features that make it easier for a computer, and forecasters, to predict a storm path.
In other cases, such as Ivan, the skies keep everyone guessing.
* * *
Forecaster Lixion Avila stared at four computer screens on Thursday afternoon, rushing to issue his 5 p.m. advisory for the hurricane center.
He clicked several buttons on his keyboard and pulled up a variety of colorful lines arcing toward Florida. The lines, each from a different computer model, generally agreed on the path of the powerful Category 4 storm over the next two to three days: Toward Cuba.
After that, they fan out like a fishtail.
"The big problems begin 72 hours out," Avila said. "When the models diverge, it's very difficult to decide where it's going."
Avila and other experts at the center review more than a dozen computer models before issuing a forecast. The models range from basic statistical compilation to complicated three-dimensional renderings that map the composition of air at 60 different levels.
Many of the models were conceived in the 1970s and 80s but became notably more reliable in the 1990s, with major advances in computer systems and weather data collection.
Some models use history as their guide, offering an idea of what storms have done in the past. But the better models generate a complicated portrait of the atmosphere and apply the laws of physics to determine what a storm might do.
None are perfect.
"Some models perform better in some storms, and some better during others," said Chris Hennon, meteorologist at the hurricane center. "It's a mystery. That's why we don't rely on one model."
Forecasters rely most heavily on about four models that have proved most accurate in predicting a hurricane's path.
All four assemble a picture of the atmosphere by taking information from weather balloons, satellites, buoys and aircraft, collecting data about wind and moisture and pressure. The computers then divide the world into roughly 60-mile grids, each offering a snapshot of current conditions.
Employing principles of physics, the models predict weather conditions such as high- and low-pressure systems that help determine the path of a hurricane, said Mark DeMaria, meteorologist with the National Oceanic and Atmospheric Administration.
Many models transmit data two to four times a day to the computers at the hurricane center in Miami. Those models are the foundation of all forecasts.
"We rely on the models more and more," said David Nolan, meteorology professor at the University of Miami. "The main role of the forecasters is to identify the trends in the models."
Some models frequently diverge from the others. Forecasters usually disregard the variant tracks as "outliers" and depend on the consensus of the programs.
The most reliable forecasting approach, in fact, is combining the most reliable models.
Those include the Global Forecast System, GFS, run by the National Centers for Environmental Prediction in Maryland; the Geophysical Fluid Dynamics Laboratory model, GFDL, run in Maryland and California; the United Kingdom Meteorological Office program, UKMET; and the Navy Operational Global Atmospheric Prediction System, NOGAPS, run in California.
Meteorologists working on one of the most respected models - the GFDL - say it has outperformed all others so far this season, with a track error rate of about 140 miles three days out.
But typically more reliable than the programs is the official forecast by the National Hurricane Center, in which human beings interpret the various computer calculations.
"The subjective forecast beats every model," said Morris Bender, a research meteorologist who worked on the GFDL.
The main limitation of computer models is that they provide only a coarse picture of the atmosphere, meteorologists say.
The models map only in large chunks, sometimes overlooking smaller features that may play an important role in forecasting.
"We have limited ability to measure the atmosphere in every place at every time," said Nolan, the meteorology professor at the University of Miami. "And the oceans are a big void."
Nonetheless, the models have significantly improved forecasters' ability to track a hurricane's path over the past decade, experts say.
"If you look at the progress that's been made in terms of accuracy, it's almost entirely due to the models," said Stephen Lord, director of the environmental modeling center at the National Centers for Environmental Prediction.
The current five-day forecasts, for example, are more accurate than the three-day forecasts a decade ago, said Jim Goerss, research meteorologist at the Naval Research Laboratory in California.
In addition to using models that simulate the atmosphere, forecasters also look at more basic statistical models that tell them how past storms have behaved.
These models are not nearly as accurate at predicting a storm's path. But one, the so-called SHIPS model, is best at forecasting a storm's intensity, one of the weakest aspects of hurricane forecasting.
By Thursday afternoon, the models were still in disagreement over whether Ivan would clobber Florida. They were, however, in slightly better agreement than previous runs, forecaster Avila wrote in his report.
"But the track continues to be uncertain," he wrote, "and models diverge."
- Jamie Thompson can be reached at jthompson@sptimes.com or 727 893-8455.
Appears all the models have it going to FL.
===============================================================
Hi SM,
Thankfully, not all of them are in agreement. Some of the models start to diverge after exiting Jamaica.
If you're interested, the following article presents a good explanation of why that is happening....
Where will Ivan go?
By JAMIE THOMPSON
Published September 10, 2004
Millions of Floridians reeling from two hurricanes are anxiously awaiting the answer to one simple question:
Is Ivan coming here?
The best estimate of the National Hurricane Center in Miami is based on a half-dozen computer models that analyze millions of pieces of data from England to California.
But even with the aid of technical measurements such as wind radii and stepped microwave radiometer data, hurricane prediction still involves some educated guesswork.
Some models say Tampa Bay may be in danger. Others point to the east coast. Still others spiral it away from the U.S.
While it's always difficult to plot a hurricane's path more than three days out, Ivan is particularly confounding to the models.
"I think there's more disagreement with Ivan," said Ernie Jillson, meteorologist with the National Weather Service in Ruskin. "After Ivan passes Jamaica, the models spread out - some off into the Gulf of Mexico, others east near the Bahamas."
In the past three days, the forecast tracks for Ivan have zigzagged across the state. With every shift, fear ripples through communities on all sides of the skinny lines.
"There's always a certain amount of disagreement in any storm, when you get out in the four, five day time frame," said Robert Molleda, meteorologist with the hurricane center. "For Frances, the models seemed to be in a little better agreement over farther time frames. But with Ivan, we're still seeing divergence."
The reason, experts say, are variables in the atmosphere. Sometimes it has distinct features that make it easier for a computer, and forecasters, to predict a storm path.
In other cases, such as Ivan, the skies keep everyone guessing.
* * *
Forecaster Lixion Avila stared at four computer screens on Thursday afternoon, rushing to issue his 5 p.m. advisory for the hurricane center.
He clicked several buttons on his keyboard and pulled up a variety of colorful lines arcing toward Florida. The lines, each from a different computer model, generally agreed on the path of the powerful Category 4 storm over the next two to three days: Toward Cuba.
After that, they fan out like a fishtail.
"The big problems begin 72 hours out," Avila said. "When the models diverge, it's very difficult to decide where it's going."
Avila and other experts at the center review more than a dozen computer models before issuing a forecast. The models range from basic statistical compilation to complicated three-dimensional renderings that map the composition of air at 60 different levels.
Many of the models were conceived in the 1970s and 80s but became notably more reliable in the 1990s, with major advances in computer systems and weather data collection.
Some models use history as their guide, offering an idea of what storms have done in the past. But the better models generate a complicated portrait of the atmosphere and apply the laws of physics to determine what a storm might do.
None are perfect.
"Some models perform better in some storms, and some better during others," said Chris Hennon, meteorologist at the hurricane center. "It's a mystery. That's why we don't rely on one model."
Forecasters rely most heavily on about four models that have proved most accurate in predicting a hurricane's path.
All four assemble a picture of the atmosphere by taking information from weather balloons, satellites, buoys and aircraft, collecting data about wind and moisture and pressure. The computers then divide the world into roughly 60-mile grids, each offering a snapshot of current conditions.
Employing principles of physics, the models predict weather conditions such as high- and low-pressure systems that help determine the path of a hurricane, said Mark DeMaria, meteorologist with the National Oceanic and Atmospheric Administration.
Many models transmit data two to four times a day to the computers at the hurricane center in Miami. Those models are the foundation of all forecasts.
"We rely on the models more and more," said David Nolan, meteorology professor at the University of Miami. "The main role of the forecasters is to identify the trends in the models."
Some models frequently diverge from the others. Forecasters usually disregard the variant tracks as "outliers" and depend on the consensus of the programs.
The most reliable forecasting approach, in fact, is combining the most reliable models.
Those include the Global Forecast System, GFS, run by the National Centers for Environmental Prediction in Maryland; the Geophysical Fluid Dynamics Laboratory model, GFDL, run in Maryland and California; the United Kingdom Meteorological Office program, UKMET; and the Navy Operational Global Atmospheric Prediction System, NOGAPS, run in California.
Meteorologists working on one of the most respected models - the GFDL - say it has outperformed all others so far this season, with a track error rate of about 140 miles three days out.
But typically more reliable than the programs is the official forecast by the National Hurricane Center, in which human beings interpret the various computer calculations.
"The subjective forecast beats every model," said Morris Bender, a research meteorologist who worked on the GFDL.
The main limitation of computer models is that they provide only a coarse picture of the atmosphere, meteorologists say.
The models map only in large chunks, sometimes overlooking smaller features that may play an important role in forecasting.
"We have limited ability to measure the atmosphere in every place at every time," said Nolan, the meteorology professor at the University of Miami. "And the oceans are a big void."
Nonetheless, the models have significantly improved forecasters' ability to track a hurricane's path over the past decade, experts say.
"If you look at the progress that's been made in terms of accuracy, it's almost entirely due to the models," said Stephen Lord, director of the environmental modeling center at the National Centers for Environmental Prediction.
The current five-day forecasts, for example, are more accurate than the three-day forecasts a decade ago, said Jim Goerss, research meteorologist at the Naval Research Laboratory in California.
In addition to using models that simulate the atmosphere, forecasters also look at more basic statistical models that tell them how past storms have behaved.
These models are not nearly as accurate at predicting a storm's path. But one, the so-called SHIPS model, is best at forecasting a storm's intensity, one of the weakest aspects of hurricane forecasting.
By Thursday afternoon, the models were still in disagreement over whether Ivan would clobber Florida. They were, however, in slightly better agreement than previous runs, forecaster Avila wrote in his report.
"But the track continues to be uncertain," he wrote, "and models diverge."
- Jamie Thompson can be reached at jthompson@sptimes.com or 727 893-8455.
Dan 
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