Tropical trouble? Joaquin poses flood threat

An East Coast storm threat

The 2015 Atlantic hurricane season has been quiet overall -- plenty of storms, but generally weak ones. This can be traced back to the near-record El Nino taking place in the Tropical Pacific. But, as we often say: "All it takes is ONE to make for a bad hurricane season." This one has the potential to be bad for some part of the East Coast.

An extreme pattern

Of course, people want to know exactly where a storm is going to hit, how strong it will be and how bad the rains will be. It's too far ahead to go into those details. But that doesn't mean we should stay quiet about potential and the overall pattern that is setting up. Let's look at that pattern.

When we talk about "patterns," we're usually talking about conditions high up in the atmosphere. Meteorologists use the level close to 20,000 feet above the ground (for reasons not important here). We also look for "anomalies," or changes from the average pattern. With that in mind, here's the upper-air map for Saturday morning from the European model -- the world's overall best.

The colors show the extremes. The red and purple in Canada represent extremely high pressure. And the dark blue in Georgia represents extremely low pressure. This is a classic "blocking pattern." Past patterns like this have led to disastrous flooding in many parts of the world. Meteorologist Stu Ostro of The Weather Channel has done a lot of research into these patterns, which seem to be happening more in recent years. No one should want this pattern to verify. Even a weaker version would likely lead to serious flooding somewhere along the East Coast. We can't say WHERE the floods will occur, but the POTENTIAL is there.

The main U.S. model, the GFS, like other models we saw today, shows an extreme pattern, too -- but not as extreme as the European.

Oh, yeah ... The storm

We often get so focused on a storm or hurricane that we overlook the pattern. So that's why I started with it. The storm gets too much credit for the disastrous results. If it weren't for the extreme blocking pattern over the North Atlantic, the name "Sandy" would be just another one of hundreds of names of hurricanes that curved out to sea. The block is what caused the left turn that led to the disaster.

This storm is still being affected by the El Nino, as so many others have this season. The wind shear becomes too strong in the Atlantic storms, when there's just too much wind at high levels in the atmosphere. So, Joaquin will struggle to strengthen, even though it's over very warm ocean. But with massive high pressure to the north, the pressure difference (or "gradient") will be big, leading to strong east winds up and down the coast. They'll be piling water up to the coast. The stronger the winds and the larger stretch of ocean they cover (the "fetch") will determine how much coastal flooding and beach erosion will result. And it doesn't help that we've had already huge amounts of coastal flooding and beach erosion in some parts of the East Coast in the past week.

Stay tuned for another update tomorrow.