As powerful Hurricane Isabel lumbers across the Atlantic, the unaswerable questions loom. Where and when will it hit?

Forecasts indicate the Category 5 hurricane will hit anywhere from Maine to Florida, anytime from Wednesday to Sept. 22. The real answer, according to the official forecast from the National Hurricane Center: "The hurricane could pose a significant threat to the U.S. East Coast, (but) it is too early to speculate what portions of the U.S. East Coast might be affected."

Hurricane forecasts have improved a great deal in recent years. The hurricane center went from a maximum three-day forecast to a five-day forecast this year after proving the longer-range prediction was accurate within a range of about 325 miles. That means if the computers predict a storm's center will hit Savannah in five days, it's likely to hit somewhere from Jacksonville to Myrtle Beach.

The latest five-day track has it about 450 miles east of Palm Beach, Fla., Wednesday morning.

Every hurricane reacts uniquely based on the weather conditions surrounding it. A high pressure ridge likely to set in north of Isabel is the key this time, according to the National Hurricane Center. It should keep Isabel from curving directly north, away from the U.S. coast. Instead the curve should be slowly northwest, toward the Carolinas.

The other method for predicting hurricane paths is based on history. Isabel was born off Africa and has taken a direct western path toward Puerto Rico. That is similar to hurricanes Hugo (1989), Andrew (1992), Bertha (1996), Fran (1996) and Floyd (1999). Hugo made a beeline for Charleston. Andrew straightened out after a brief curve north and slammed Miami. The others skimmed the South Carolina coast before hitting North Carolina hard.

"All we know now is we could be threatened," said Steve Rich, meteorologist at the Charleston office of the National Weather Service.

Once Isabel begins to curve -- probably Sunday or Monday -- forecasters will have better ideas where it might hit. Even then, though, exact landfall is difficult to predict.

"It could very well be one of those storms that parallel the coast, like Floyd or Fran, where we might not know until a day or two, or even a few hours ahead of time, where exactly it's going to come in."

Of course, even a brush with a big tropical system can cause major problems, such as the flooding in South Carolina as Floyd settled over North Carolina.

One other problem with forecasting Isabel is there is little precedent with Category 5 storms, which have winds of more than 155 mph. Hugo briefly hit Category 5 and made landfall at Category 3. Only two storms since then have reach Category 5 status -- Andrew in 1992 and Mitch in 1998. Andrew caused $26 million in damage in Florida and Louisiana. Mitch killed 9,000 people in Central America.

On the positive side, Gov. Mark Sanford shouldn't have any difficulty persuading coastal residents to evacuate should Isabel head this way.