ALL EYES ON SALLY IN THE GULF WHILE THERE’S GOOD NEWS FROM THE EASTERN ATLANTIC
FROM BRYAN NORCROSS - Sunday, September 13, 2020: Sally is a serious threat to the northern Gulf coast from south of New Orleans east to Pensacola. The storm is forecast to be a significant hurricane when it reaches the coast Monday night or early Tuesday, but it's expected to be crawling at that time, so the assault will begin during the day Monday and only slowly let up when the storm is well inland on Wednesday.
The coastal areas of southeastern Louisiana and Mississippi are extremely vulnerable to storm surge. The current forecast is for the Gulf water to be pushed 7 to 11 feet above the normal high tide level across southeastern Louisiana north and east along most of the Mississippi coast.
The giant levee system surrounding the City of New Orleans should not be challenged by this surge, but areas outside of the flood protection system and along the Mississippi coast will be inundated if the storm intensifies as forecast and moves slowly inland across southeastern Louisiana or into Mississippi.
The water will rise in the inland waterways as far east as Panama City in the Florida Panhandle, although the storm surge there is not expected to be extreme. A height above normal high tide of 1 to 3 feet is forecast.
The swells from Sally will start to push the water higher along the northern Gulf coast on Monday.
Rainfall will be another issue from the Florida Panhandle to Louisiana. The slow-moving storm is forecast to produce widespread 6 to 12 inches of rain with isolated areas receiving 20 inches across the north-central Gulf coast. Fresh-water flooding is a serious threat on top of the storm surge.
The upper-level winds may become less supportive of strengthening just as the storm approaches the coast, which hopefully will keep the system to a Category 2. But given the known uncertainties in intensity forecasts, residents there need to be ready for at least a Category 3.
Needless to say, it’s a very dangerous situation.
Elsewhere in the tropics, in the western Gulf, there’s still a slight chance that Disturbance #1 will acquire an organized circulation and become a tropical depression. It would likely stay in the western or southern Gulf and there’s no indication it would get very strong.
Paulette continues to intensify and is taking aim on Bermuda. It is expected to arrive there on Monday. The current National Hurricane Center forecast is for it to be a strong Category 2, so they need to prepare for a Category 3. The good news is, Bermuda has a lot of experience with hurricanes, and is generally built to withstand them.
Tropical Depression Rene is barely hanging on, and will likely die over the next few days in the central Atlantic.
The disturbance that we have been a bit concerned about in the eastern Atlantic was able to consolidate enough to be designated Tropical Depression Twenty. That turns out to be good news. Since it now has organization, it’s likely to intensify and be able to take advantage of the pathway north created by Paulette and to a small degree Rene.
If it had stayed weak, if might not have been able to use that path and continued tracking to the west toward the Caribbean. The steering for stronger storms is at a higher level in the atmosphere than for weaker ones. So in this case, stronger is better.
Tropical Depression Twenty will likely become Tropical Storm Teddy, and is forecast to become a hurricane as it heads north into the central Atlantic.
It appears that Disturbance #2 will lag far enough behind probably-Teddy that it can organize and intensify as well. The next name on the list would be Vicky, if things develop in that order. The expectation is that it will move north into the eastern Atlantic and not be a threat to land.
Disturbance #3 now becomes the system to watch. The computer forecast models do not intensify it quickly when it moves out over the ocean tomorrow. If those forecasts are correct, it will be more likely to travel west toward the Caribbean islands over the next week or so. It’s too early to know more.
There’s another system behind Disturbance #3, but the atmosphere should slowly be shifting to a fall pattern in the next couple weeks as cold fronts start pushing farther south. So it's possible we won't have to deal with that.
No threats to South Florida are expected to develop through this coming week, at least.