It is rather doubtful, forecasters said, that Isabel will veer harmlessly out to sea as some hurricanes have done in the past after threatening the coastline.
Hurricane forecasting has improved dramatically over the past 10 years. Powerful new computer models have been created to incorporate finer grids of weather information from satellites and other sources.
Isabel remained a dangerous Category 5 storm Sunday with top sustained winds of about 155 mph.
Nature achieved perfection Friday when Isabel's winds reached similar high speeds, making the Atlantic storm a Category 5 on the Saffir-Simpson scale of intensity. This strongest of all possible classifications mean Isabel would cause maximum damage if it comes ashore.
Sunday afternoon the storm was about 370 miles east-northeast of the Turks and Caicos Islands, moving toward the west-northwest near 12 mph. This general motion is expected to continue into mid-Monday.
Various computer models using different methods are used to forecast the storm's path. On Friday, the models were in disagreement, meaning forecasters could not yet say where the storm would go with any confidence.
"Unfortunately, the models are now in excellent agreement with Isabel Making landfall along the central U.S. East Coast in about 4 days," forecaster Stacy Stewart said Sunday.
The storm may fluctuate in strength in the intervening days. It is common for strong storms to weaken and strengthen at various times during their travels across the ocean.
Not since Andrew devastated parts of Florida in 1992 has a Category 5 storm come ashore in the United States. Hugo in 1989, at Category 4, was the second costliest storm ever, behind Andrew. Hugo inundated coastal regions of South Carolina. The only other Category 5 storms recorded making landfall were Camille in 1969 and an unnamed storm in 1935.
The last Category 5 storm in open water was Mitch, in 1995. It weakened before coming ashore but still killed 11,000 people in Central America.
As with all hurricanes, Isabel is a gargantuan area of low atmospheric pressure, with winds rotating counterclockwise as viewed from above. It is fed by ocean water that's warmer than 82 degrees Fahrenheit (28 Celsius). Pressure is lowest at the center of the storm, pulling air at the surface inward.
This churns the sea into a frenzy of waves and spray, feeding ocean water into the storm.
The air rushes upward near the storm's center and flows out the top as if from a chimney, allowing more air to rush to the storm center.
Isabel is headed toward even warmer water early in the week, so forecasters do not expect any significant weakening soon.
Days before Isabel makes landfall, coastal residents up and down the eastern seaboard can expect large seas and crashing waves to announce the coming of the storm.
The Atlantic hurricane season began June 1 and ends Nov. 30.
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