Hello all. For sake of blog content and organise my own thoughts as a weather nerd I thought I'd post this ramble about a developing situation in the US. This one is Hurricane Ida, which for a while looked to be a potential Katrina part II. It's a bad hurricane and there's a long way to go before landfall happens around midday tomorrow US time, but thankfully despite its track and strength New Orleans should just about be able to weather it.
However if the hurricane over-performs - and it is possible - the situation could be every bit as bad as Katrina. Here's my thoughts...
So we have a concerning situation for the gulf coast and New Orleans as Hurricane Ida makes her approach to central Louisiana. I've been following this system since it was a tropical depression south of Jamaica way back earlier in the week, and even back then it showed worrying potential. Initially it was predicted to cross the Yucatan, weaken, and then power up again to hit Mexico or southern Texas. Then gradually as it crept more and more in a north-westerly direction towards Cuba the forecast models swung around past Houston to point at the Florida panhandle, before swinging back again to centre on New Orleans - a forecast track from which it has barely shifted over the past few days.
At first the models were mildly concerning, predicting a Category one to two landfall. However the danger quickly became more evident as several factors came into play. One was a ridge forming over Florida that would effectively lock the track in place and prevent it from landing more harmlessly in the underpopulated Florida panhandle. The second was a lack of forecast sheer in the gulf north of Cuba. Sheer is what disrupts hurricane formation, though sometimes in rare cases coming in at the right angle it can ventilate and strengthen development. The atmosphere over Cuba was moister than usual, meaning dry air intrusion wouldn't be too significant, and dry air is the other main factor that helps choke off hurricane development. Then - and this was arguably the most dangerous factor - there was a bath-tub warm eddy of water right on the forecast track, an eddy that ran deep and would provide an ample reservoir to help a hurricane rapidly intensify. Not only that, but unseasonably warm shelf waters south of New Orleans would help any approaching hurricane to maintain and even increase intensity as it climbed out of the gulf and on to land.
The problem was that this threat was rather nebulous and difficult to communicate for the National Hurricane Centre. Though it was still a tropical depression, it was moving fast and as soon as it moved to the warm water just south of Cuba it would explode into a tropical storm, a storm which would weaken only slightly as it passed over land thanks to the largely flat lands and sparse mountains of western Cuba. Once on the other side if still intact it had ample fuel to feed on. The concern was that if Ida could maintain her basic structure as a tropical storm she could power up to be a category three hurricane by the time she landed ashore on Sunday on the gulf coast.
Unfortunately, Ida managed to achieve hurricane status SOUTH of Cuba, and crossed as a minimal category 1.
This was really concerning. The forecast models for intensity were now showing high-end Category 3's and 4's for landfall. One even showed a Category 5, the maximum a hurricane can achieve. Small mercy then that Ida remained a modest in size at only a third the width of Katrina, and that a train of dry air off of the mountains of Cuba wrapped into her core delaying her intensification. The category forecasts swung back in the main to a borderline Category 2 / 3.
However things are changing again now. Ida has begun to hit the eddy. She's mixed out the dry air and has managed to wrap around her core of convection, beginning the formation of an eye and setting the stage for rapid intensification. However she's doing so a tad slower than anticipated As such the National Hurricane Centre are predicting a strong high-end Category 3 hurricane set at 130mph moving towards Houma, about 50 miles South West of New Orleans. Unfortunately the forming eye of Ida appears to be a little right of the track, setting her to possibly brush the west side of the big easy. As the strongest side of a hurricane is the north eastern side, this is very concerning indeed. During Hurricane Katrina New Orleans was hit by the weaker western side, which meant far lower winds - though the storm surge generated by the far larger Katrina was around 19ft for the city - and 33ft for Gulfport and Biloxi to the east of her.
Ida isn't Katrina sized, thankfully. The storm surge currently forecast for her is 10-15ft south of New Orleans, and 7-11ft in Lake Pontchartrain which borders New Orleans. Thanks to the new defences installed in NOLA, she is rated to survive a Category 3 hurricane and though the levees may overtop new ground mats installed at the base of the levee walls mean that they should not erode and breach. However a mandatory evacuation has been sounded for everyone outside the levees, and a voluntary evacuation for everyone within New Orleans. The super-dome once again is taking people in for shelter.
There are a lot of unknowns. Will an Eye Wall Replacement Cycle cause Ida to collapse her newly forming eye in an attempt to create a newer, wider one? That would broaden the size of the hurricane causing a greater push of water but weaken its wind-speed dramatically. Will she rapidly intensify as predicted, hitting the Category Four 140mph windspeed NHC forecast earlier today before the downgrade? The next twelve hours should set things in stone. Although currently not looking Katrina catastrophic, Ida does look to be the meanest and most dangerous hurricane in a long while for Louisiana and once again, all eyes are on New Orleans.