Cristobal continues to meander over southern Mexico. Its winds are slowly diminishing since the center is over land — it will likely be downgraded to Tropical Depression Cristobal today. Meanwhile, it continues to dump epic amounts of rain. The weather pattern will finally begin to change late today or early tomorrow, opening the door for what’s left of Cristobal to head to the north.
Generally speaking, the forecast is straightforward. A strong dip in the jet stream is going to set up over the western Gulf of Mexico, and a high-pressure system will strengthen over the Atlantic. Between them, a south-to-north channel will open up, taking Cristobal and the mass of tropical moisture around it to the north.
The other thing in which we can be confident is that the system that approaches the northern Gulf coast over the weekend will be very large and lopsided. The strongest winds and the heaviest rain will be on the Florida side – the east side – of the center of the system. In this kind of situation, where the center makes landfall is often irrelevant because the strongest winds and heaviest rain are far removed from the center of the storm.
Cristobal is currently embedded in a separate, large rotating weather system, which is acting like something of a cocoon. That large system – the so-called Central American Gyre – is a large circulation that also has a tremendous amount of tropical moisture associated with it. The well-defined flow that will develop over the next couple days will pull the whole mass of wind and moisture – Cristobal and the Gyre – to the north.
The open questions are the details. How much of the core of Cristobal – the concentrated thunderstorms near the center of the circulation – will survive its trek over land the next couple days? Assuming the core is significantly disrupted, to what extent will it be able to regenerate when it moves north? How will the somewhat-unfavorable upper-level winds affect the system as it moves to the north? Will it be able to reorganize with the energy focused near the center, or will the energy spread out over most of the eastern Gulf and Florida?
When the combo system of the large gyre circulation and what remains of Cristobal moves north, it will most likely remain a broad circulation. Residents along the northern Gulf should be ready for the strongest winds to be displaced far to the east. They could impact Alabama and the Florida Panhandle, for example, even with the center coming ashore in Louisiana, plus or minus. In addition, if the system is unable to consolidate, the moisture channel from the tropics into the system’s center might well cover some or all of the Florida peninsula.
The bottom line: We cannot concentrate on the center of the storm. We are sure the worst weather will be to the east of where the center crosses the coast. The only question is, how far east?
Everybody from eastern Texas to the Florida Panhandle should be ready to be affected by this storm. Even over the Florida Peninsula, we will likely get some heavy rain over the weekend and/or next week. It will be a big, sprawling system, but we can’t know yet how heavy the rain will be on the fringes, which may well include South Florida.