The birth of a monster storm

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The following is a typical monster-storm scenario.

The following is a typical monster-storm scenario.

It is winter and we’re in the Bahamas. Far out in the northwestern part of the continent a huge mass of cold air begins sweeping southward and eastward. The cold air pressure is high and, as it pushes forward, its

leading edge slides under the warm moist air before it. This creates low pressure and southwesterly winds well ahead of the front, and dumps rain and snow into the advancing cold front.

Up and down the East Coast, pretty TV news people are laughing into the cameras and talking about whether the cold air will arrive before or after the weekend. The relatively few people out at sea are anxiously watching because they know that this is no laughing matter.

A high-pressure ridge seems anchored over the southwest North Atlantic and it stubbornly slows down the marching front as it approaches the coast. But the ridge begins to weaken, as they all do eventually. Warmer air with lower pressure drifts up from the Caribbean. The front senses what it needs to continue on.

As the cold air sweeps over the relatively warm waters of the Atlantic, the winds increase, first from the southwest and then from the west and northwest after the front and its phalanx of storm passes. Up off CapeHatteras, the winds cause huge waves to build and break over the shallow waters extending far out in the ocean. The proximity of the Gulf Stream fuels the conflict, because its waters are warm, as is the air above. Down off South Florida, the Stream is even warmer, and just a few miles off the coast. Here again, the wind is stronger than over land. As the front approaches, the winds moaning out of the southwest stop and grow silent.

Suddenly, a force of air from the northwest hits like a moving brick wall. Seas begin to build rampantly as the Gulf Stream races ever northward, bucking the new winds. Soon the waves of the Stream crash and tower like drunken skyscrapers. They clash from all directions sending geysers cascading vertically into the air, tumbling back down onto the face of the ocean as crushing tons of water.

The cold air then roars over the Bahamas banks. These are thousands of square miles of shallow water warmed by tropical sun. The ocean around them is thousands of feet deep. The warm air over the banks adds more fuel to the fury. But that high-pressure area that used to sit over the Bahamas hasn’t gone away completely; it’s only retreated south and, unwilling to die, struggles to rebuild. As it does so, and as the cold front encounters increasingly warmer waters, it slows. A battle line covers thousands of miles as the two conflicting systems struggle for dominance, each trying to push back or absorb the other.

On the sea’s surface, waves and boats are irrelevant pawns in the struggle. The front stalls with water spouts, squalls, thunder and lightning.

Skippers downloading weather graphics see that the frontal line is beginning to become occluded in two areas. Rather than sweeping on as a smooth curved line displayed in the earlier graphics, each of these areas indicates a slowing down and doubling back along parts of the frontal line. One area is off to the northeast of the Bahamas. More significant for those in the Bahamas is the one over the Gulf of Mexico. They know what this probably means, and the information coming in a few hours later confirms it. The doubling back has become a local counter-clockwise circling of weather. And it’s not going to just sit there.

As the hours pass, the system’s rotational speed increases and it begins to move along the now almost stalled frontal line. The low heads northeast, across the Bahamas, where wise skippers have already hunkered down in safe holes. As the front had approached they knew the wind directions to fear: first southwest and then west and northwest clocking to northeast. Now they’re not sure, because it’ll depend on where the Gulf of Mexico-spawned low passes relative to their positions. The wind could be from any compass point and of varying velocities. The frontal line is like a highway to hell, drawing the rotating low along. As the high pressure to the north behind the front pushes it against the air to the south, the frontal line wavers, and so does the track of the growing monster storm. Just a small change of course in the overall scheme of things can make life-and-death differences to people on boats that will be, depending on the direction of the wind, anchored behind protective shores or exposed to lee shores.

Some of the boats don’t make it. Their skippers have guessed wrong (It’s hard to always be right when you’re a pawn to cosmic giants) or maybe they just didn’t pay enough attention. We’ve seen it repeatedly over the years. This seldom makes the glossy tourist magazines, I suppose because it’s perceived as not being good for business. But it happens over and over again.

Trained meteorologist will realize I’ve left out other factors that would also influence this drama. There isn’t space here for it all — and besides, I don’t know them all. I’m just a tiny player, watching in awe, trying each day to understand a little more about this show.