Early this morning, Hurricane Delta made a direct hit on the resort areas of Cancún and Cozumel in Mexico. Top winds in circulation were estimated to have been 110 mph when the Delta’s center crossed the shoreline. The prediction was the tides would surge to 6 to 12 feet above normal, varying over different parts of the Yucatán coast. Obviously, it will take some time to know what has happened, but damage is likely.
Thankfully, slightly hostile upper winds knocked Delta down from a Category 4 to a Category 2 in the hours before landfall. This is proof that subtle, unforecastable atmospheric changes can affect and change storms with small-diameter circulations quickly. Still, based on everything we know, a super-supportive atmospheric environment for reintensification is forecast to return as the center of the storm moves back over water this afternoon.
The fact that Delta has a small core allowed it to intensify incredibly quickly in the first place. Mother Nature doesn’t have to work as hard to get a small circulation rotating super-fast compared to a large one. But still, Delta pegged the needle on quick spin-ups. Delta’s eye was measured at only 5 miles across, a so-called pinhole eye, which only very strong hurricanes have.
That small core will likely continue to be disrupted a bit over land but is expected to reorganize and restrengthen later today and tomorrow over the warm Gulf waters. In addition, over time, the reorganizing process is forecast to result in a larger-diameter storm. It probably won’t be as strong as it was, but high winds will be spread over a larger part of the Gulf.
Unfortunately, that’s bad news. The larger the diameter of the storm, the greater the storm surge on the northern Gulf coast. Think of a full bathtub. Push the water with your hand, and you splash some water around. Push it with your forearm, and you can push a lot of water out of the tub. A bigger storm is like a longer forearm and produces a higher surge.
It now appears that Delta will arc fairly far west in the Gulf, perhaps slightly deflected by the remnants of Tropical Storm Gamma, which are barely identifiable just to the west of the hurricane. This longer path will delay Delta’s approach until Friday, and give it a bit more time over water to strengthen and grow.
Also, the water farther west in the Gulf is warmer all the way to the coast. Hurricane Sally stirred up the Gulf closer to Mississippi, Alabama, and Florida, noticeably cooling the near-shore waters there, but that’s not where Delta is tracking.
So all of this is bad news for the Louisiana and Mississippi coasts, with effects extending as far east as the Florida Peninsula.
Because of the large shelf of shallow waters offshore of the northern Gulf states, the entire coastline is extra-vulnerable to storm surge. The Gulf water piles on top of the shelf and spreads inland. Dangerous storm surge is likely well outside the high-wind zone to the right of where the center of Hurricane Delta comes ashore – likely including at least the Mississippi coast and to a lesser degree in Alabama and the Florida Panhandle.
The consensus of the computer forecast models and the National Hurricane Center forecast brings Delta ashore in Louisiana. It’s too early to know exactly where, but the steering flow seems pretty well established, so we’re not dealing with another drifting storm with no clear path.
The longer, arcing track has delayed the Hurricane Watches and Storm Surge Watches for the northern Gulf coast, but they will be issued today.
As Delta approaches the coast on Friday, the upper-level winds should become somewhat more hostile, and the storm itself will stir up some cooler water as it approaches the coast. As a result, it is forecast to be weakening, but still be a tremendously damaging storm. The increase in diameter will make up for any decrease in wind speed as far as damage potential.
After Delta makes landfall, dangerous flooding rains will spread inland across the South. Late in the week into early next week, what’s left of Delta is forecast to move through the Midwest eventually arc out to sea across the Mid-Atlantic.
Needless to say, full preparations will be required in the threatened areas. Pay very close attention to local emergency instructions.
Nothing else is in the offing in the tropics, at least into next week.