• Bryan Norcross

CRISTOBAL STARTS ITS MOVE NORTH – SOUTH FLORIDA TO FEEL THE FRINGE EFFECTS

Cristobal has spent more than a day over land, which has significantly disrupted the circulation of what was the tropical storm. But this is an odd situation. The tropical storm has been embedded in a larger low-pressure system called the Central American Gyre. So even though the core of the former tropical storm is dying out, the broad, related circulation still exists, so the overall system will likely regenerate and strengthen, at least somewhat, once it gets back over the Gulf water.

A strong dip in the jet stream is setting up over the western Gulf and at the same time high pressure is strengthening over the Atlantic. Together they are creating a strong channel for what remains of Cristobal and the larger Gyre circulation to move north together. That movement is slowly beginning, and should pick up in earnest later today.

Once the weak version of Cristobal and the Gyre clear the Mexican land mass, the system is expected to reorganize and intensify, at least to some degree, over the next couple of days. Its circulation will be large, and large systems are slower to strengthen because there is more air to get moving. Also, the atmospheric conditions do not appear especially conducive over the Gulf of Mexico for dramatic strengthening.

So the system will move north as a large, very wet circulation, but storms like this can cause a lot of problems. A tremendous amount of tropical moisture is going to stream north over the Gulf Coast and Florida. Southeast Florida will be on the fringe, which means that surges of tropical moisture will be pulled over us, reinforcing what’s here. Add to that a front that will push in early next week, and the rain will likely pick back up, even as Cristobal’s influence dies. It’s the rainy season on top of the rainy season.

June is one of the two rainiest months in South Florida because northern systems – like the dip in the jet stream lifting Cristobal north – draw tropical moisture from the south. Voilà! Here we are. September is the other most rainy month, but that’s because it is when we’re most likely to be affected by purely tropical systems coming from the east.

There is always a tendency with hurricanes and tropical storms to focus on the cone. But the cone reflects the forecast for the center of rotation of the system. In a broad tropical system like Cristobal is expected to be over the Gulf, the center is not especially relevant. The strongest winds and most persistent rain are likely to be well east of the center because of the sprawling former-gyre origins of the system. All residents from Louisiana to Florida and inland in the Southeast should pay attention to local alerts.

The wet weather in South Florida will come in waves into next week. Even as Cristobal moves inland over the Southeast U.S., we might stay in a persistent moisture tail. So the main effect will be the potential for local flooding due to persistent periods of rain.

Thinking about the rest of the hurricane season, Dr. Phil Klotzbach at Colorado State University, where seasonal hurricane forecasts were pioneered, updated their projections for the hurricane season. The new forecast calls for 19 named storms, including the three we’ve already had.

That’s 16 more, which is not that crazy since on average since the beginning of the 90s, the first storm hasn’t shown up until June 22nd. If the rest of the season produced 16 storms, that would barely be above the modern average. So don’t get carried away with the numbers.

In any case, it is time to prepare. Let’s do it now.


© 2019 by Bryan Norcross Corporation

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