They called it The Bulge. Satellites from several sources detected the anomaly nearly simultaneously, but it took another month to convince the lay-person citizenry that this was a real threat.
Sea level in the Atlantic is never uniformly flat. The moon above has a lot to do with that, tides and all. People understand tides as coming in, going out. Sure, sometimes a 'king tide' is unusually high, or a storm surge will push flood waters inland a hundred yards or so, but the water always recedes, right? Tides always go back out.
Until they don't.
Six teenage girls calling themselves the STEM Squad, geniuses each, warned that this would not be the case when The Bulge arrived. They even gave a date. April 16th, give or take twelve hours.
Naturally there were those who laughed. Much of the coastal population of the Carolinas, Georgia, and Florida went about their business as usual. Indeed, half of the coastal population in Florida mocked the warnings that the Bulge was a uniform rise of the Atlantic Ocean surface level of more than 45 feet, moving steadily southward like a storm cloud, six hundred miles wide. Others described it as being like a towering dust storm stretching from horizon to horizon and barreling towards you at speed.
Cold water melting from the Arctic and Greenland built up underneath, near the ocean floor, pushing the Bulge up and away toward the southern Atlantic.
When it began swallowing islands in Nova Scotia and the Maritimes, evacuation notices were given for the entire coastline of Florida. Miami residents had until April 16th to move permanently, or become food for sharks.
That gave them five weeks.
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Based on Shakespeare's Timon Of Athens