He warned of power outages and storm surge flooding, with Monday's full moon meaning higher tides, as well as "the heaviest October rains ever recorded in the Northeast U.S." as Sandy's moisture-laden air collides with arctic air from Canada.
However, "there remains quite a bit of uncertainty with the track," according to the National Weather Service.
Also, forecasters have trouble estimating the staying power of a storm as it loses hurricane strength, Masters blogged this afternoon.
The storm was northeast of Cuba this morning with sustained winds of up to 110 m.p.h., and heading northward, threatening to blast the Bahamas by Friday morning.
Its track is likely to stay off the east coast of Florida, as it remains a hurricane into the weekend.
What happens next is where computer models diverge.
It could move westward, clipping North Carolina early Monday morning, possibly while still a hurricane, or hang farther east, weakening back into a tropical storm - but still packing winds of 39 to 73 m.p.h. - before its path threatens landfall farther north.
Earlier today, several computer models suggested Sandy might stay well offshore till Maine or Nova Scotia.
No official warnings or watches had been issued as of this morning for anywhere north of Georgia. A hurricane warning was in effect for Cuba and the Bahamas, with tropical storm warnings and watches for the east coast of Florida and southeastern Georgia.
As of midafternoon, the regular forecasts for Philadelphia and even Atlantic City still weren't sounding ominous, simply mentioning "a chance of rain" for each day from Saturday to Wednesday, ranging from 30 percent (Saturday and Wednesday) up to 70 percent (Sunday night).
Contact staff writer Peter Mucha at 215-854-4342 or firstname.lastname@example.org.