Re: Irene Post-Mortem -- Why isn't dry air able to be forecast well?
Posted by
weathercritic on 8/29/2011, 4:48 pm
Obviously if I'm raising the topic, dry air was being entrained. What I'm trying to address is why it was not anticipated as being a primary source for weakening of the system. We all know that dry air can weaken a system. In the case of this system, dry air was being given a back seat to shear and lower SSTs, and from my vantagepoint -- hence the topic -- the dry air was a major reason why the system deteriorated. What I'm trying to address is why this catalyst for deterioration was not given a more significant role in the forecast.
There are 35 advisories, and of the most recent (numbers 20-35), only 24, 28, 29, 30 and 32 address dry air. In most cases those references were observations of effect, not predictions of effect. 24 refers to dry air having an effect only in passing (meaning the ultimate significance of its role was not anticipated); beyond that half-sentence, that's as deep as the explanation goes.
As I have already said, my interest in this is not related only to Irene. This is a frequent occurance, where dry air has a significant impact, but was not *forecast* as being significant.
The caps are the NHC shouting -- I don't know why they do that -- turn the caps lock off, NHC! It's about time.
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HURRICANE IRENE DISCUSSION NUMBER 32
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
500 AM EDT SUN AUG 28 2011
SATELLITE AND RADAR IMAGERY SHOW THAT DRY AIR IS NOW WRAPPING INTO MUCH OF THE SOUTHERN SEMICIRCLE OF IRENE
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HURRICANE IRENE DISCUSSION NUMBER 30
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
500 PM EDT SAT AUG 27 2011
... [DRY AIR ENTRAINMENT] ...
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HURRICANE IRENE DISCUSSION NUMBER 29
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
1100 AM EDT SAT AUG 27 2011
... [DRY AIR ENTRAINMENT] ...
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HURRICANE IRENE DISCUSSION NUMBER 28
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
500 AM EDT SAT AUG 27 2011
THIS SUGGESTS THAT DRY AIR SEEN IN WATER VAPOR IMAGERY TO THE WEST OF IRENE IS STARTING TO ENTRAIN INTO THE HURRICANE.
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HURRICANE IRENE DISCUSSION NUMBER 24
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
500 AM EDT FRI AUG 26 2011
THIS...ALONG WITH THE CURRENT CYCLONE STRUCTURE AND DRY AIR ADVECTING TOWARD THE HURRICANE IN WATER VAPOR IMAGERY...ARGUE AGAINST SIGNIFICANT STRENGTHENING.
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