posted on Aug, 19 2008 @ 08:20 PM
Anyone that knows me knows that for a few years I have been saying the National Hurricane Center official advisories are BS. Prior to Hurricane
Andrew the NHC would use a value of 65% to 90% of flight level winds to determine surface sustained winds. Post Andrew and the move to political
correctness (making storms look worse than they are) the NHC went to a system of using straight 90% to determine surface sustained winds. I have
stated over and over that this doesn't work. I have used the lack of any supporting surface observations as evidence. Well I now have better
Yesterday on my climate blog I reported buoy observations as reported by the NDBC.
"Buoy" SANF1 which was near the center of circulation reported a sustained wind of 50mph but at 45 meters off the ground. SMKF1 reports 57mph at 49
KYWF1 which is right by SANF1 only reported a sustained wind of 19mph at the same time SANF1 reported 50mph. KYWF1 is at 6.4 meters. VCAF1 reported a
sustained wind of 17mph at the same time SMKF1 reported 57mph. VCAF1 is at 6.4 meters as well. So there is obviously a significant drop in wind speed
from 45-50 meters down to 6.4 meters.
The numbers came directly from the following data source...
At the time the buoy observations were logged the NHC was reporting the storm with sustained winds of 60mph. This storm passed right over the areas
where the buoys were. The buoys were both on the strong side of the center of circulation. Sustained winds close to what the NHC reports were
observed at 49 meters above sea level. Wind reports near the surface in almost the exact same locations were significantly less. This indicates
a great deal of loss from 50m down to 5m.
There was a program on television about the tornado intercept vehicle that was able to get into a tornado and take a wind reading. Being able to match
it up to radar readings taken from a truck nearby they were able to determine a loss of about 10 to 20% for winds at the surface. This is the
difference between winds at the surface and winds just above the surface.
How can the NHC say there is a 10% loss from flight level when the loss from 100 meters and down is even greater?
With this storm over land I have hunted high and low for reports that matched what the NHC said. I find none. I have yet to find a wind gust equal
to the sustained wind reports. Okeechobee, FL which was on the very right side of the eye reported a sustained wind of 38mph and a wind gust of
58mph. This was at the time the storm was reported as having 65mph sustained winds. Assuming the NHC actually found a FL wind of 65kts they would
have reported sustained winds of 65mph (I say if and I'll show why shortly). If they used the 65% rule instead of 90% rule they would have reported
sustained winds of about 46mph with wind gusts of about 60 to 65mph. That would have been believable. There would have been surface observations to
more or less support that report. You will find this to be the case in about every storm. Take the FL winds and go with 65% and you'll find a real
number that will be backed by surface observations.
The 49m and 6.4m buoys prove the NHC method doesn't work. The surface observations prove the NHC method doesn't work. If you go back to the old
system and just use 65% as the rule you'll get accurate reports. There will be some exceptions where the dynamics of a storm might justify going a
bit over 65%. Maybe to 75%. But for the most part I have found that 65% is the most accurate.
There was more I was going to add to this but after about 10 interruptions where I am I forgot what I was going to include. :-)
Oh yes here is a quote from a NHC discussion yesterday. They admit they fudge on the numbers.
WE HAVE BEEN CARRYING 45 KT FOR THE CURRENT INTENSITY SINCE EARLIER
TODAY ALTHOUGH THERE HAVE BEEN NO RECENTLY OBSERVED FLIGHT-LEVEL
WINDS TO SUPPORT THIS VALUE.