Is Entrainment of Cool, Dry Air "Killing" Isabel?

[wxman57]

Take a look at the latest water vapor imagery:

http://home.houston.rr.com/wx/dryair.gif

Note the 3 areas of very dry air. The pocket of dry air just southwest of Isabel is trapped, and it looks like it's already being drawn inside. But more important is the short wave approaching Florida from the west. See that southward bulge in the dry air across the NE Gulf? That's heading west on an intercept course with Isabel. Now look along the east U.S. coast. There's a COLD front out there, folks! Look at the dew points in the 50s along the Carolinas and VA coast. It's 61-64 degrees across eastern NC now, and I"m talking temperature NOT dew point here.

http://adds.aviationweather.noaa.gov/da ... fc_clt.gif

I don't see the NHC or Steve Lyons mentioning this cool and, more importantly, dry air that is in Isabel's path (and actually moving toward Isabel). What will this mean for the future of Isabel? I think the effects are already evident in the latest IR imagery:

Isabel 5:24pm CDT:
http://home.houston.rr.com/wx/isabelbefore.gif

Isabel Now:
http://home.houston.rr.com/wx/isabel.gif

What you will notice is that Isabel's bands appear to be opening up. The eye, which was evident earlier, is not nearly as tight. Convection which was bright red and yellow earlier has weakened considerably and has expanded outward.

AHA! Just as I'm typing this, Steve Lyons is noticing this. He's pointing to the trend in IR imagery that shows Isabel is NOW weakening.

Now take a look at what dry air can do to a storm in about 6-8 hrs:

Hurricane Gordon prior to dry air intrusion:
http://home.houston.rr.com/wx/gordon21.gif

Hurricane Gordon 6-8 hours later:
http://home.houston.rr.com/wx/gordon24.gif

Gordon was basically destroyed in short order by dry air. And I think that the same thing may have just begun with Isabel. Now this isn't to say that Isabel would dissipate before landfall, but pressures could be rising sharply overnight, and Isabel may not be able to maintain hurricane strength by tomorrow with no convection near the center. So keep hoping, NC residents. The dry air may be your salvation if it keeps infiltrating the storm.

[wxman57]

Steve Lyons just gave a special report, talking about the dry air intrusion and the fact that residents along the east coat COULD get very lucky if the current trend continues. I agree, such dry air intrusions can destroy a hurricane overnight.

[Rainband]

Lets hope so!!! Great OBS as always

[abajan]

You know, the writing was on the wall for days now. But some folks persist in making this system into a monster.

Oh well, different strokes for different folks I guess.

[John]

wxman, I believe you are right, dry air mass is heading toward Isabel also looks like dryer air is getting entrained into the circulation center as the convective envelope is starting to spread in a wider banding fashion. This will have a major impact on the Hurricane since most of the convection should start to spread away from the core resulting in major weakening. Im betting Recon is going to come in with rising pressure let's wait and see. But you have something here this is really happening, what great news.
John

[Stormcenter]

Wxman57 that was an excellent post. Thanks!

[ColdFront77]

Jim Cantore mentioned shortly after 11:00 PM Eastern that it was quite cool with a northeasterly wind in Nags Head, North Carolina.

[WEATHER53]

Everyone in the weather community knew that the cold front would be moving thru late Monday and I have to believe they knew dry air would follow it yet there was not one bit of previous attention paid to it but rather all the emphais on how the resultant, following high would force the storm to a nw move. How could this fact of the dry air after frontal passage have been missed. Seems like a looming huge blunder. Thanks

[tundra]

This is really good news! I hope that it comes to pass.

[Guest]

More likely it is a huge over reaction to the dry air theory by folks who dont know any better

Everyone in the weather community knew that the cold front would be moving thru late Monday and I have to believe they knew dry air would follow it yet there was not one bit of previous attention paid to it but rather all the emphais on how the resultant, following high would force the storm to a nw move. How could this fact of the dry air after frontal passage have been missed. Seems like a looming huge blunder. Thanks

[WEATHER53]

Ok, Dave, thanks but the water vapor does look dry. Can you detail the counter view to this dry air info on this post. Thanks.

[Guest]

that was a nice hypothesis... but a couple of things...

did we go through this once before? was the dry air suppose to Kill off Isabel this morning then this afternoon?

the analogy to Gordon is kind of stretch... Gordon was MUCH closer to the coast and MUCH smaller in size and was barely at any time a cat 1 hurricane. Arguably Gordon was not.

Moreover arent you carrying the point too far? aren't MOST east coast Mid or late sept hurricanes surrounded by dry air as the near the east coast?

Didnt you also declare Claudette dead in the Gulf too?

[SacrydDreamz]

Isabel has strengthened since this morning.. maybe the dry air is aiding in development!

[Derek Ortt]

Gordon was definately a hurricane as recon had 98KT at flight level (not sure if it was 850 or 700mb, if it was 700mb, it should be reclassified as a cat 2 based upon the new science of 90% reduction from that level).

However, Gordon was much smaller and the air was much cooler than this air. I cannot see this weakening below hurricane intensity before reaching the coast as systems of this size do take a long time to spin down.

Also, doesn't this structure resemble Bonnie quite a bit. I would say Issy looks light years better than Bonnie when Bonnie was in this location

[JetMaxx]

I may be proven wrong, but from what the model data is indicating, Isabel will begin to accelerate NW toward the coast in response to the large high pressure moving off NE coast/ into Canadian Maritime provinces -- with a return moist SE flow propelling Isabel toward the coast.

If it occurs as when Opal made landfall, to the right of that hurricane will become unbearably muggy and humid -- as it did here in Georgia during Opal. I was living in Jackson, Mississippi at the time where it poured rain with a cool and gusty north wind -- but dewpoints here in Georgia east of Opal's track were well into the 70's...it was like a steambath (according to my family members who were living here then).

FYI - I'm not some "wishcaster" who forecasts every hurricane to be extreme. If I'm guilty of anything, it's using past hurricanes as my guide....in this situation with Isabel, I see similarities to the synoptic setup of hurricane Hazel in 1954, the Long Island Express hurricane of 1938, and hurricane Hugo...

I'm certainly not a degreed meteorologist who knows all the hows and whys of the atmosphere...I'm more of a historian with growing ability to interpret model data and recognize patterns that created monster hurricanes of the past; but I'm certainly no Chris Landsea or Hugh Willoughby. Hell, until this week I didn't even know what an annular hurricane was

[AussieMark]

JetMaxx - Do you agree that all Hurricanes are different but some may follow a smililar path.

Hazel-Hugo similar with Hazel further North.

[JetMaxx]

What I mean is that both hurricane Hazel in 1954 and Hugo in 1989 both accelerated toward the Carolinas as Isabel is going to do within the next 36 hours.....

The weather patterns are similar....hurricanes approaching the Carolina coast while turning and accelerating between high pressure to the east and a strong digging trough approaching from the west -- which served to funnel the hurricane rapidly toward the coast while also becoming more intense (both Hugo and Hazel were cat-4's).

That is my concern...since the synoptic weather pattern is almost the same, that Isabel will also intensify into a monster as it accelerates toward the Carolinas.

[AussieMark]

Is Isabel in the Gulf stream now?

When is the shear expected to recede.

[wxman57]

Dry air entrainment has certainly halted Isabel's intensification overnight, though she appears to have recovered slightly. But latest WV imagery shows that the main dry air pocket has moved across Florida and there's very little moist air ahead of Isabel. Temperatures are now in the 50s across the Carolinas and Virginia just inland of the coast. Isabel certainly hasn't ingested any of THAT kind of air in the past day or two. This is cool, day air at the surface, not just some mid-level dry air over the tropics. I see that the NHC sure sees the dry air "problem" now.

I'm still very confident that the cool air now flowing toward Isabel will lead to significant weakening prior to landfall, but that doesn't mean those of you on the coat in Isabel's path should relax. Hurricane forecasting is not an exact science. Isabel could still be a hurricane when it hits. But I don't think the chances are good of it increasing in intensity. We should have a good idea about landfall strength later today as the air over the mid Atlantic coast flows into Isabel.

[Aquawind]

Temperatures are now in the 50s across the Carolinas and Virginia just inland of the coast. Isabel certainly hasn't ingested any of THAT kind of air in the past day or two. This is cool, day air at the surface, not just some mid-level dry air over the tropics. I see that the NHC sure sees the dry air "problem" now.

There certainly is a cool dry breeze out of the NNE. Of course the Outer Banks are holding things up near the water.

http://www.rap.ucar.edu/weather/surface/sfc_clt.gif

Looking at the big picture of WV doesn't look all that dry. I have seen drier enviroments with intensification. It's the combination of cool and dry that may hinder strengthening. Shear may play a part as well it seems.

http://cimss.ssec.wisc.edu/tropic/real- ... wg8sht.GIF