Isaac Impacting The Gulf Coast (Updated)August 28th, 2012 at 9:15 am by Jeremy Wheeler under Weather
(See update at the bottom)
Isaac has really gone against the odds, and so far has remained a tropical storm. After the 5am update, however, it developed a ragged eye structure. So the storm is probably now a hurricane. The latest update had the storm with winds of 70 mph which is really only 4 mph from the cutoff to be a hurricane. The storm’s pressure dropped to 977 mb (millibars of pressure). It was located about 180 miles south/southeast of Biloxi, MS. I used to live down there in Ocean Springs (next to Biloxi) back before Katrina devastated the region. I still have yet to see how it is after Katrina, but I’ve heard it’s started to build back in the last couple of years. Anyway, numerous rain bands were already pushing onshore ahead of the storm:
The storm has been fighting periodic punches of dry air which has kept the system weaker than many of the computer models showed for the past 2 days. The European model, however, has been doing a great job since Isaac’s early formation. It had it in about its current location and at about this strength 3-4 days in advance. It has become a very powerful long-range forecasting tool. Hurricane warnings are up from the central coast of Louisiana to the Mississippi/Alabama border. The storm is big, but it is not like strong hurricanes in the past. In fact, to me it feels like this storm is still a little overdone. The rainfall forecast is an impressive 6-8″ with some areas expecting over 15″.
If the storm really slows down, then maybe I can see it. But the radar has shown much more of a broken structure up until the last couple of hours. The forecast is for Isaac to slow down, but it is still moving at a pretty good pace to the northwest at 12 mph.
The storm surge forecast is something that I don’t get right now. I looked at some of the buoys from NDBC. I found one buoy that had waves up to 15ft, but that is out over the open ocean. So far this storm has only been a tropical storm. Hurricane Katrina was a category 5 storm which weakened to a cat 3 upon landfall in 2005. It’s highest surge was 20ft, but that was a completely different storm. Before they did case-by-case the National Hurricane Center would expect a category 2 hurricane to produce a surge of 6-8 feet. At the moment they are expecting a total water rise up to 7-12 feet from southeast Louisiana over to the Mississippi Coast. They do figure that Isaac will come in at high tide, so I guess that is total water rise (surge and tide combined) and not just surge. Is the natural tide that high right now? I think there are several TV forecasters that are saying that the surge is 8-12ft, but that is not correct. Here is a graphic about it from the NWS office in New Orleans. Remember hurricane Ike was a category 2 hurricane when it made landfall over Texas. It’s surge was high enough to go overtop of the 17 ft seawall in Galveston. But it was a very large storm. Isaac is also a large storm, but nowhere near as powerful. So I’m not saying anyone is wrong, but I just wonder how they get the numbers. There is a model that they use called the SLOSH model. It is specifically for surge. So maybe the model is showing a strong surge at high tide. Remember too, bathymetry is a big factor in water levels. The surge may push in to Lake Pontchatrain and cause flooding. That was what Katrina did in 05′ when it toppled the levees. I wonder if that will happen now though with Isaac’s more westerly track and weaker winds. There was a hurricane Lili back in 2002 that was a powerful hurricane, but it made landfall more towards central Louisiana. So there were very little impacts on New Orleans. That storm was compact, and the core of it moved over a less populated area. However, I believe that played into some people’s decision not to evacuate during Katrina. Because before that hurricane the media made it look like the worst was going to happen. In a post-Katrina world now though you can’t be too careful.
The latest track takes Isaac about 20-30 miles west of New Orleans. It wobbled west this morning, but I’m not sure if that was a temporary wobble or a permanent shift. Either way that would still put the city on the bad side of the storm. Winds upon landfall are forecast to be about 85 mph near the center:
This is expected late tonight into early tomorrow. After landfall it will steadily move northwest and weaken over land to a tropical storm. It will then start to bring beneficial rain to places like Texas, Arkansas, and Missouri. The models are in pretty good agreement, but there has been a small shift to the west in the last few hours:
Here locally we will have a cold front moving through and an area of high pressure behind it. That should keep Isaac far to our west over the next 3 days. It will also bring us some scattered showers and storms later this afternoon into tonight.
Behind the front we’ll see a few showers early Wednesday. Then nice weather should move in. In fact…On Thursday I am expecting some really nice weather around here as dry/sunny weather finally settles into the region.
Some of the moisture from Isaac may head our way by next Sunday along the next cold front, but I’m sure the timing will change before then. Stay tuned for the latest updates on Isaac and on the local weather.
(UPDATE 11:00am…I said that Isaac would have some curve balls in its forecast days ago…Well…It is still a tropical storm in the 11am update. Winds remain at 70mph. The pressure Dropped 1 mb.)
(UPDATE 12:30 pm….The Hurricane Hunters flew into the storm and found some hurricane force winds. Hence Isaac has been upgraded to a hurricane in a midday update.)
Meteorologist: Jeremy Wheeler