PENSACOLA, Fla. – Call it cloudy with a chance of tar balls.
TV forecasters along the Gulf Coast have been adding a new ritual to their daily weather lineup — predicting the path of oil spewing from the Deepwater Horizon rig. But predicting the oil's movement is proving more difficult than predicting sunshine or showers.
"It's the biggest challenge in forecasting simply because it's all new," said Jason Smith, a meteorologist at the Fox 10 station in Mobile, Ala. "I've tracked a lot of hurricanes, but this is the first oil spill I've had to track."
Forecasters began adding the slick to the outlook soon after the Deepwater Horizon rig exploded in April, but their initial success was spotty. The oil didn't move as quickly as meteorologists predicted, and residents in some areas like the Florida Panhandle spent days anticipating oil before it appeared.
Even though BP PLC cut off the oil flow for the first time last week, forecasting oil's landfall will remain a challenge for months as the sticky stuff continues to wash up.
One fact that can make oil forecasting more difficult, meteorologists say, is that there are fewer data-collecting instruments out at sea than on land. Buoys and weather instruments attached to oil rigs provide eyes for forecasters, but with enormous ocean expanses to cover, patchy instrument coverage can leave forecasters blind in places.
For help, weathermen have turned to the National Oceanic and Atmospheric Administration, which has been producing daily 24-, 48- and 72-hour forecasts noting where the spill is likely to be next.
NOAA's maps, made using modeling software and data from daily overflights by helicopters and planes, note the spots where the oil is likely to be most concentrated. But the maps aren't perfect, and forecasters have a particularly hard time predicting the path of tar balls, which are harder to detect than oil sheen.
"One of the things about forecasting oil spills is it's pretty easy to show when you're wrong because there are a lot of people out there looking at it," said Doug Helton, who oversees the map production from NOAA's Seattle office.
With oil, he said, everyone wants to know how much will arrive and where. And when forecasters are wrong, they hear about it.
"If you forecast a rain storm and you know it only rains 5/8ths inches of rain instead of an inch of rain then no one really complains," he said, not so with oil.
That's one reason TV forecasters sometimes add their own analysis, though NOAA's map is indispensable.
The meteorologists scour a NASA satellite picture of the actual slick. They pore over tide tables because tides help push oil into bays and rivers. They study currents, winds and heavy seas that also affect the oil's movement.
"As a meteorologist I look at the winds and I look at the waves," explained Margaret Orr of WDSU in New Orleans.
Many forecasters have improvised, taking standard maps and adapting them as they go to generate their oil spill graphics. Some make their oil blobs green, others red or even a realistic brown.
The Alabama forecaster Smith — who doubles as WALA's fishing and outdoors reporter — has used a NASA satellite image in the past to help predict good fishing spots. Now he uses the same image, enhanced with the computer program Photoshop, to highlight oil sheen for viewers. Producing the oil images means more work each day, but his forecast segments now run a minute longer than pre-spill, about 3½ minutes.
Viewers, meanwhile, have responded to the maps and graphics with additional questions, forecasters said. One frequent question: whether a hurricane could suck up oil and drop it on their homes. The answer is 'no,' because hurricanes only drop evaporated fresh water.
Meteorologists admit that while they are knowledgeable about wind and waves, they are still learning when it comes to the fine points of oil slick forecasting.
Allen Strum, chief meteorologist at the ABC station WEAR in Pensacola, said meteorology school didn't include a class on oil spills, though he recalls taking one on oceanography.
"I never ever anticipated that I would be talking about a forecast of junk on the water and where it was going," Strum said.