Sunday, August 26, 2012

Mandatory Evacuations- South Florida


-Fort Meyers Beach
-Bonita Beach
-Big and Little Hickory Islands
-Black Island
-Lover's Key
-San Carlos Island

NEW GFS Brings 2x More Rain to New Orleans Than Katrina

If the new GFS were to verify, Hurricane Isaac could bring 2 TIMES MORE rain to New Orleans than Katrina did. Looking at the graphic above, we see that there were a few instances of 7.0 to 9.9 inches of rainfall where Katrina made landfall on the left graphic. There are only a couple reports of 10.0 to 16.3 inches immediately along the Gulf Coast where Katrina made landfall.

On the right graphic is a total precipitation map until Hour 93 of the new GFS. It shows over 12 inches hitting much of southeast Louisiana, with a maximum amount of just over 20 inches shown on the extreme bottom right corner of the image.

If the levees keeled over in 2005 with Katrina due to 10 inches of rain (among other factors), imagine what 20 inches of rain in a large Category 2-3 hurricane could do.

I am not saying this will happen, this is only meant as a comparison and should be treated as such.



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