Boris Konon
EF4
The GPS dropsondes, introduced in the late 90s, and the SFMR in the early 00s, were a game changers in many regards into terms of high-density wind obs in TCs.
You get measurements of multiple atmosphere parameters from this dropsonde during its entire descent time. And one thing this does is to give us a better measurement of center pressure. We get a wind reading at splashdown along w/ the pressure in the eye. The rule of thumb is for every 10 kt of wind at splashdown within the eye, you can subtract 1 mb. This is esp. important in TC w/ tiny eyes, as hitting the exact wind center is not easy.
The SFMR gives us remote measurements of the sfc winds much better than what we used to do, such as taking 85-90% of the max FL winds (usually 10k ft), and stating that was the surface max wind. We know now that does not always work well, as TC structure is variable. As a result, we are seeing both significantly higher and lower winds at times compared to what we would have had just using winds at 10k ft and doing a standard reduction. So when you hear of “winds never recorded before” or “record high winds” you need to put a “*” next to it and note that improved technology has *allowed* us to now accurately measure what has always been
there! It's not much different than when DOWs were introduced and showed us wind speeds from tornadoes we always suspected were there.
The SFMR does have its share of issues. One is it does not work well when shoaling is present. Also, there have been calibrations issues w/ the algorithms over the years. We had found is that it has a high bias once winds get to about 80 kt, and the higher the wind, the more biased high so by the time you get to 130-140 kt, it is too high by 15-20 kt.
This has been acknowledged by NOAA and so last year, SFMR winds on NOAA aircraft stopped being reported. On Air Force recons, it is still reported, but it is same instrument and the bias high for intense TC is very apparent. If you look at vortex messages from the Cat 5s this past season, you'll see at times very high SFMR winds, higher than the FL winds, which is a red flag something is off. NHC has not used these values for assigning max winds.
Before this issue was caught, some intense hurricanes were clearly too high. For instance, Dorian in 2019 -- 910 mb pressure w/ 160 kt winds. That is too high IMHO. Gilbert had 888 mb and was given 160 kt, Wilma 882 mb and 160 kt, and Melissa 892 mb and 160 kt, and all 3 had tiny eyes and were in the deep tropics. Dorian was at 27N and had a large eye, so that pressure-wind relationship does not jibe w/ empirical observations in other hurricanes significantly stronger in pressure, or this means we are significantly too low for winds for many historical intense hurricanes! I think max winds of 145-150 kt for Dorian is more reasonable.
