Sunday, August 26, 2012


This is The Weather Centre's official forecast for Isaac. The Weather Centre is not related to, or affiliated with the National Hurricane Center. In the event of an evacuation order, always heed NHC warnings over our advice.

This is the official forecast for Tropical Storm Isaac. We will start out with what is making the forecasts so hard to get together.

This is a 500mb chart for 96 hours out. I highlighted two things- a trough disturbance in the Northeast, as well as Tropical cyclone Isaac. We are watching the trough to see if it influences Isaac. If Isaac happens to be in a situation where the trough does influence the system, Isaac would likely make a more easterly landfall.
However, if the trough does not take control of Isaac and goes on its merry way, Isaac would be free to go west, like many new models and ensembles have been saying in the past 24 hours. This is definitely more concerning, as we are now seeing cities like Houston, Texas and New Orleans, LA under the gun. Let's take a look at these ensembles and models.

We'll start with the NCEP ensemble group. This is from 6z, as opposed to other ensemble groups that I will be posting soon that were made at 0z- six hours earlier. Anyhow, these ensemble members are showing a varied landfall anywhere from Houston, Texas to the end of the Florida Panhandle. There does seem to be some middle ground in the Louisiana/Texas border, but the members are just too spread out to confirm that.
I think that this is a perfect example of the trough not influencing Isaac. The ensembles seem to see that the influence will not occur, thus a more westward movement will begin. I do not want to speculate on the extreme member scenarios, such as the lone member showing a Houston landfall.

This is a chart of the 0z CMC Ensembles. You can partially see a consensus of the members, bringing Isaac to New Orleans. However, note the few members also hitting Houston. I don't know if you can see that through all of the disorganized and messy lines on this image, but there are a few more members hitting Houston than there are in the NCEP, and this is concerning. It is also worrying for New Orleans, with such a tight consensus compared to the NCEP.

Lastly (and possibly the scariest) is the FNMOC Ensembles. The FNMOC Ensembles are derived of the NOGAPS model, and these two are made by the Navy. The FNMOC Ensembles are taking a tighter consensus than either of the above groups to hitting the Texas/Louisiana border, and threatening Houston ten-fold over the NCEP. Given, the NOGAPS is not a good model, therefore the FNMOC Ensembles may not be either. However, given that the models have been shifting west, one can only believe that this is a logical solution (which it very well could be).

So, the ensembles are marking out targets between the extreme west Florida Panhandle down to Houston, with a favored track hitting Louisiana and in the New Orleans area. Let's take a look at the 0z model suite.

The 0z model suite is split down the middle, with some models projecting a Florida/Alabama landfall, and others hitting Louisiana head-on. I'll just cut to the chase here. Given that Isaac is still a tropical storm and has not significantly strengthened, I am siding with the western models, as the Coriolis effect that moves storms north when they are strong appears to be working against Isaac, who remains fairly weak. Thus, a more westward movement would be anticipated.

It should be noted that the ECMWF, which originally anticipated a Louisiana track, has shifted east to join the eastern camp in their solution.

Here is a quick sketch of my track and intensity forecast. I believe Isaac will stay weak for a bit before strengthening into a Category 1 hurricane. The waters are not as warm now as they can be during the tropical season, so Category 2 strengthening should occur immediately prior to landfall. I am going with a western solution due to a very good ensemble consensus, with some models also supporting this.


Credits: NCEP/EMC for Ensembles, UW-Milwaukee for Late and Early Models


WinterStorm said...

The latest GFS is even farther west than that! These models just keep shifting west...

Here's the latest GFS run: Link

Isaac could really have some Rapid Intensification when he reaches the Gulf. Hopefully he doesn't slow down too much when he enters the GOM. I'm starting to get worried for New Orleans. If Isaac makes landfall in NO as a CAT 3+ Hurricane, it would be EXTREMELY BAD. This is the last thing that they need. And Wednesday is the 7th anniversary of Katrina. Also, check out hour 102 on the latest GFS. It shows Isaac still sitting there 2-3 days after landfall. This would mean MAJOR flooding. Sorry about the long comment, and have a good day!

Andrew said...

WinterStorm: Sorry for getting back so late. Great article, no worries on the long paragraph. The more the merrier!

WinterStorm said...

Isaac is trying to form an eye, but dry air is getting in there. Isaac is really running out of time now... The most I can see it getting is strong CAT 1 to Moderate CAT 2. Still, storm surge and heavy rain may cause major flooding. I still can't believe that Isaac isn't a hurricane yet. I mean really, has there ever been a 982mb hurricane in the Gulf Of Mexico in August that wasn't a hurricane?