HURRICANE IRENE UPDATE – ILLUSTRATION OF AN ATMOSPHERIC SQUEEZE PLAY

This evening Hurricane Irene is looking rather impressive:

at201109_sat_2.jpg

Winds remain at 120 mph, but the pressure continues to fall, now the lowest yet at 954 mb, meaning the storm continues to strengthen, and it continues on a track just west of due northwest  at 12 mph.  It’s about 185 miles SE of Nassau, Bahamas, and 810 miles due south of Cape Hatteras, NC.  I expect this motion to continue through the night, and Irene should become a category 4 storm (130 mph+) later tonight or tomorrow (for those unfamiliar with the hurricane scale click here).

The National Hurricane Center’s official track has come a bit further WEST with it’s latest advisory at 5 pm:

They now have the hurricane barely crossing over Cape Hatteras as a category 3 hurricane and paralleling the coast about 50-60 miles offshore as a category 2 before making a second landfall off the eastern tip of Long Island.

The more important issue is why the track is coming back west.  In my previous post from two days ago I discussed how the trough over the upper Midwest and Great Lakes would eventually pull the storm northwest and then north into the Carolinas.  Often times in these situations, the trough actually rescues the coast to the north, curving the storm to the northeast and sparing places like Ocean City, MD and NYC from direct effects of a hurricane.  But there’s a little wrinkle in the setup this time.

I’ll use the upper air maps from the European to illustrate my point.  I often use this model because it flat out out-performs the other models on an almost daily basis – and no surprise, it’s doing it again.

You can see the trough coming into the Great Lakes by the U shaped lines (red line in the center). This trough will “pick up” Irene to an extent and direct it more northwest and then north in the next 2-3 days. Normally, as stated above, it would continue to carry it out to sea, northeast from the outer banks of North Carolina.

However, in this case, there’s an upper level low (the big red L above)  and pumped up high pressure ridge along the East coast (big blue line above) which will block Irene from escaping on a northeastern trajectory.  The end result is a squeeze play between the approaching trough and the ridge and upper low off the East coast.  The relative strength and position of each will determine the path of Irene. Right now, the trough is looking weaker than modeled just 24 hours ago by the American models, a common mistake as they often overestimate trough strength. As we get closer to the event, these models are having an “oh, shit!” moment and gradually correcting themselves.  I don’t think they are done correcting themselves at the moment either. And since the NHC uses a blend of the models, their track has been nudged farther west with the lastest advisory. The European model has been very persistent in showing a weaker trough and therefore less of a push off the coast.  This, in conjunction the upper level low and rather strong high pressure ridge off the East coast will result in a path in which Irene parallels the coast after landfall, as illustrated on the European surface map for next Saturday and Sunday, respectively:

You can see how the hurricane comes almost due north toward Cape Hatteras as a category 4 storm, and continuing in that direction, paralleling the coast and then crosing Cape May as a category 3 storm, then NYC as category 2 and continuing into the Hudson valley of New York, weakening to a tropical storm.  All of this effectively illustrates our squeeze play discussed above. Like I said, I don’t believe the westward adjustment is done quite yet, so don’t be surprised if the NHC’s track comes a little farther west in the next few days.

Another important factor regarding the track of Irene is the actual position of the storm right now in comparison with where it was forecasted in the preceding hours.  The storm has been riding on the western periphery of the white cone seen above on the NHC map. This makes the future path of the storm more likely to follow the western edge, allowing for a more western landfall.

All of these factors I feel point to a MOST LIKELY initial landfall of Irene at or around Moorehead City NC (25 miles or so on either side) as a strong category 3 or category 4 , then traveling over the western Pamlico and Albermarle Sounds, then over or just off the coast from Maryland to NYC, as a category 2 or 3 storm.  This has the potential to cause a large amount of destruction if this should come to fruition.  There is the chance that the trough could be stronger, or the East coast ridge could be weaker and push the storm 50 or 100 or even 200 miles off the East coast, which would still result in a lot of wind and rain.  The trough could be even weaker than modeled, and the storm could move even further west, pushing inland over North Carolina and up I-95.  But right now, that’s how I see it.

I’ll try to update as I can, but I may be boarding up my house at the shore come Friday myself.

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