Hurricane Dorian: Why is this storm so difficult to track?

Hurricane Dorian's slow movement over the past 24 hours has made predictions difficult. Meteorologists agree the powerful storm will eventually turn north, but the biggest question is when.

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Monday's 11 a.m. EDT advisory by the National Hurricane Center revealed Dorian had been downgraded slightly to a Category 4 storm, but the storm remained stalled as it pummeled the Bahamas.

The slow speed and uncertainty about when Dorian would begin to turn north prompted a Federal Emergency Management Agency official to call the storm a "long-duration nail-biter," The Wall Street Journal reported.

"The most frustrating thing is not knowing where the storm is going to go," Keith James, the mayor of West Palm Beach, Florida, told CNN.

Officials in other parts of Florida, Georgia and the Carolinas agree.

The reasons for the unpredictability lie in three factors: a Bermuda high-pressure system north of Dorian, the storm's slow speed and how quickly the storm intensified, the Tampa Bay Times reported.

What makes predicting how the Bermuda High will affect Dorian so difficult is that the system is located over water, the Times reported. Meteorologists must rely on satellite tracking, rather than the balloon soundings that are used over land, and that makes data less reliable, the newspaper reported.

Although projected paths have Dorian pulling away from the Florida coast, the National Hurricane Center said even a small change in Dorian's direction or speed could prompt landfall in Florida, the Sun-Sentinel reported.

At 11 a.m. Monday, Dorian was located 110 miles east of West Palm Beach. The storm was moving at 1 mph. If the storm increases its movement by 1 mph or even 2 mph, that would bring Dorian closer to the Florida coast, perhaps impacting more areas of the state, the Times reported.

Storms stalling appear to be a more common trend, Timothy Hall, a senior scientist at NASA's Goddard Institute for Space Studies, told The Wall Street Journal. Hall defined stalling as a storm that spends at least 48 hours in a 124-mile radius, the newspaper reported.

Hall said he did not know why that trend has become more prevalent.

"That's where we're at the edge of what we understand," Hall told WSJ.

While Dorian intensified quickly, it remains a compact storm. That makes it even more difficult for forecasters to predict its direction, the Times reported.

"A six- or eight- or 12-hour difference in when it makes the turn makes all the difference," Hall told WSJ.

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