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Hurricane Category 4 Hurricane Helene

Does anyone know why the SFMR, as opposed to the flight-level winds, is not indicating hurricane-force winds at the surface? A blend of the FL (81 knots) and SFMR (43 knots) would only support ~60 knots, not a hurricane. (The highest SFMR-derived value is actually 50 knots, but did not coincide with the peak FL winds.) Normally the NHC blends SFMR and FL data, but this time it seems to have taken the FL winds at face value, even though other data do not really support hurricane-force winds at the surface now. For the record: when I compared Helene to a nontropical low, I was referring to the observation that it seems to be deepening pressure-wise, without a corresponding increase in its peak winds.
 
Casuarina Head said:
Does anyone know why the SFMR, as opposed to the flight-level winds, is not indicating hurricane-force winds at the surface? A blend of the FL (81 knots) and SFMR (43 knots) would only support ~60 knots, not a hurricane. (The highest SFMR-derived value is actually 50 knots, but did not coincide with the peak FL winds.) Normally the NHC blends SFMR and FL data, but this time it seems to have taken the FL winds at face value, even though other data do not really support hurricane-force winds at the surface now. For the record: when I compared Helene to a nontropical low, I was referring to the observation that it seems to be deepening pressure-wise, without a corresponding increase in its peak winds.
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SFMR is known to be imperfect and often undershoots the values the NHC extrapolates.
 
Dry slot that has been impeding core development is now mixing out. When that feeder band to the east gets over the channel vertically as she moves north, y'all watch what happens.

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wx_guy said:
SFMR is known to be imperfect and often undershoots the values the NHC extrapolates.
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@wx_guy Do you have a source? I’ve heard that SFMR often overestimates winds over shallow water (i.e., the nearshore shelf) and in the strongest cyclones, but the Yucatán Channel is fairly deep and Helene is still in its formative stage. Is there any reason as to why SFMR should be discarded in this case? If not, why not blend the SMFR and the flight-level winds to get a more realistic, or plausible, value? (Another reason as to why I am skeptical: the peak flight-level winds were recorded in a rain-free area east-southeast of the centre.)
 
Casuarina Head said:
@wx_guy Do you have a source? I’ve heard that SFMR often overestimates winds over shallow water (i.e., the nearshore shelf) and in the strongest cyclones, but the Yucatán Channel is fairly deep and Helene is still in its formative stage. Is there any reason as to why SFMR should be discarded in this case? If not, why not blend the SMFR and the flight-level winds to get a more realistic, or plausible, value? (Another reason as to why I am skeptical: the peak flight-level winds were recorded in a rain-free area east-southeast of the centre.)
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Just my own anecdotal experience.
 
wx_guy said:
The new experimental cone is really shining with this storm. You can see almost all of FL, GA, and SC are in alerts and parts of AL, NC, and soon probably TN. Amazing.
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Yep, love the inland warning coverage! Long overdue but better late than never!
 
wx_guy said:
Just my own anecdotal experience.
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@wx_guy Re: SFMR, I did find the following source, which directly cites the NHC. Under no circumstances is a low bias mentioned, but only a high—most often a) due to shoaling or to b) extremes of TC intensity. So SFMR is only cited for its high bias in certain situations. Overestimation does not seem to be a significant problem. Therefore, I do not understand why the NHC apparently upgraded Helene solely on the basis of FL winds in this case. Given SFMR (maximum: 50 knots; 43 knots coincident with 81-knot peak FL wind), satellite, and radar, I think that Helene is more likely a moderate or strong tropical storm (50–60 knots) wind-wise right now, though its pressure is gradually dropping. It certainly does not seem to be rapidly intensifying; a RI hurricane with pressures in the 970s mb would likely exhibit a well-defined, closed or near-closed eye, as well as a more symmetrical convective pattern.
 
Blountwolf said:
If you were to write a scenario for intensification, you'd be hard pressed to give it a better chance at it than Helene has.
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Helene, do. not. slow. down. More speed. (Sorry, Georgia.)
 
Academic arguments - it looks like an organizing tropical cyclone. No, not rapidly intensifying at the moment, but organizing. There IS a dry air slot currently - that's not up for debate, it's on the satellite image. It's likely a result of winds going across the Yucatan, and it's mixing out and won't be a factor on its trip across the gulf. Whether the SFMR or flight level winds support it being a hurricane is also a totally academic argument - in 12 hours, no one will care whether it was really a hurricane right now at this moment.

I hope I'm wrong, it sucks in a bunch of dry air, decouples and falls apart - but it's not bloody likely and I trust the NHC over anyone else on that call.
 
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