Based on everything we know, a slow-motion disaster will start today, peak tomorrow, and last into Wednesday along the southeast Louisiana, Mississippi, and possibly the Alabama coast. Damaging effects will be felt well inland as well.
Tropical Storm Sally is slowly organizing and strengthening. It is forecast to reach hurricane strength by the time the center reaches the coast tomorrow. Exactly how strong it will be is an open question. The storm still has a short window of time in fairly conducive atmospheric conditions. Residents need to be ready for a formidable hurricane.
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Worse than the strength of the storm, however, will be the duration of the high winds on the coastline. High winds over an extended period can do more damage than somewhat stronger winds that come and go.
The current forecast is for a Category 1, but the National Hurricane Center acknowledges that there is significant uncertainty in that prediction. Residents and emergency planners need to be ready for a Category 2, at least.
Even with that, the worst of this storm is not likely to be the wind. Sally’s slow crawl as it nears the Louisiana or Mississippi coast will exacerbate the other impacts of the storm as well.
The Gulf water is forecast to be pushed as much as 7 to 11 feet over normal high tide levels, in part because the storm is moving slowly. The water is pushed onshore for a longer period in a slow-moving storm, so the surge builds up.
Water rise will occur as far east as the inland waterways around Destin and Panama City in the Florida Panhandle, although there it’s not expected to be life threatening if people don’t get caught in it. The forecast is for 1 to 3 feet of water above normal high tides.
The rainfall forecast keeps increasing. Now, with a stronger storm creeping ashore, up to 2 feet of rain is forecast, with widespread amounts of about a foot from the New Orleans Metropolitan Area to Pensacola and the western Panhandle. Heavy rains will move well inland through the rest of the week, and that water will have to drain to the coast, aggravating the flood threat.
The slow movement of the storm also adds uncertainty to the forecast. Storms move slowly because the steering currents are weak, but that means that small factors can change the path. As we saw in Hurricane Laura, a small shift in the landfall point makes a big difference in how much storm surge occurs at points near where the center comes ashore.
If the center moves over or west of New Orleans, Sally could cause higher winds in the heart of the city than Katrina, which tracked to the east and slammed the Mississippi coast. The Katrina disaster was due to the flood-wall failures prompted by the storm surge.
The post-Katrina New-Orleans-area levees and flood protection system should not be challenged by Sally, but the areas outside those giant levees are at significant risk. Depending on the exact track, some of the levees protecting smaller communities may be topped.
Full hurricane preparations in the entire impact zone need to be completed immediately. And all residents must carefully follow local instructions. There is a large-scale effort underway to keep people safe.
Elsewhere in the tropics, Disturbance #1 is no longer expected to organize into a tropical depression. It will just be an area of disturbed weather in western and southern Gulf of Mexico.
Hurricane Paulette is moving past Bermuda after passing directly over the island early this morning. The entire island was in the eye. The storm was estimated to have top sustained winds of 90 mph at the time of landfall, which was a little less than forecast. We’ll have to wait for word on how they did.
Tropical Depression Rene is gasping its last breath in the middle of the Atlantic, and is not a factor.
Tropical Storm Teddy has formed out of Tropical Depression Twenty in the east Atlantic. It is still trying to get organized, but is forecast to eventually become a strong hurricane as it follows a path north into the central Atlantic carved by Paulette and, to a slight degree, Rene.
The disturbance on its heels is now Tropical Depression Twenty-one. This one is forecast to lift north and briefly strengthen into a tropical storm. It is not expected to threaten land.
If it gets named, it would be Vicky. There are no "U" names, like there are no "Q", "X", "Y", or "Z" names either. So there are only 21 names on the list. If we use them all up, like we did in 2005, they’ll start the Greek alphabet: Alpha, Beta, etc. (Did you notice that the English word “alphabet” comes from the first two Greek letters?)
Disturbance #2 will be our next system to watch in the east Atlantic. The consensus of computer forecast models is that it will slowly move toward the Caribbean islands as a relatively weak system. Air flowing out of expected-hurricane Teddy may create a hostile upper-wind environment keeping it from strengthening.
For now, it’s a long way away and forecast to move slowly, so it’s nothing to worry about. It should take a week just to get to the Caribbean, if it ever makes it.
Even with all these systems running around, no tropical threats to South Florida are expected to develop this week.