Among all 25 cat 4-5 U.S. landfalling hurricanes, Harvey tied for 14th lowest pressure
Posted by Chris in Tampa on 8/26/2017, 4:39 pm
They may adjust the pressure in the future, so that is subject to change.

https://twitter.com/philklotzbach/status/901454599541805058


If you look at the sonde that measured 938mb:
http://hurricanecity.com/recon/recon.cgi?basin=al&year=2017&product=sonde&storm=Harvey&mission=20&agency=AF&ob=08-26-0218-05-938-10-
It's a little confusing.

Here is what the 10pm CDT NHC advisory has last night:

"The minimum central pressure just reported by an Air Force Reserve
Hurricane Hunter aircraft is 938 mb (27.70 inches)."

I don't know where to find raw Air Force sonde data, but the text message that HurricaneCity processes was not coded properly when it was posted on NOAA's server. With NOAA's I think I can get the raw data usually.

Here is the sonde decoded in my system:



The mandatory levels section has 938mb as the surface pressure. The wind reading was listed as unavailable. Air temp and dew point were available there. In the significant levels section the surface wind, air temp and dew point are also normally reported. Thing is, that section coded the surface as 940mb.

When a reading is not available for the surface, the raw text message is supposed to use slashes ("/") as the wind reading when reporting the surface wind in the mandatory levels section or the significant levels section.

If the surface pressure was 940mb, 938mb would be not far above the surface. The significant levels section actually has a wind speed for 938mb, yet the mandatory levels section did not have that wind. You either have it or you don't. It should either appear in both places or both sections need to be coded with slashes. So there is some kind of error.

Notice that the air temp and dew point at 938mb in the mandatory level section are the same, to the tenths place, as the 940mb surface on the significant temperature and dew point section. That might be a coincidence.

The 938mb may have been incorrectly added to the mandatory levels section as the surface, when in reality, 940mb was the surface and 938mb was the last pressure surface wind was reported.

This is an example of a sonde that reported correctly:
http://hurricanecity.com/recon/recon.cgi?basin=al&year=2017&product=sonde&storm=Harvey&mission=18&agency=NOAA&ob=08-25-1923-18-960-124-
No wind at surface, but air temp and dewpoint was available. The significant levels section was coded properly.

I had to delete a sonde today that was not accurate, with a pressure of 859mb, that came from the prior Air Force flight. I think it terminated early and then it was incorrectly coded as being at the surface. So sometimes they are coded wrong. Sometimes they don't make it all the way down. The wind tears them apart or another error.

The vortex message had 938mb and they reported 10 knots of surface wind:
http://hurricanecity.com/recon/recon.cgi?basin=al&year=2017&product=vortex&storm=Harvey&mission=20&agency=AF&ob=08-26-021540-02-938-117%28117%29-111

If that is true, the surface for the mandatory level section didn't report wind in the sonde, even though there was. Both parts of the significant levels section had 940mb listed as the surface pressure, which was wrong. So there would be three things wrong.

If 938mb was reported as the surface level pressure incorectly in the mandatory levels section, that would be the only thing wrong.

Obviously, this was reviewed by multiple people before the NHC used it and they would have access to the raw sonde data, so it may very well be that it was 938mb. But, it's possible it wasn't. They review things for the tropical cyclone reports they do, so we'll see.
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Harvey now a tropical storm. "However, an extremely serious flooding event is unfolding." - Chris in Tampa, 8/26/2017, 2:44 pm
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