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General Discussion >> Hurricane Ask/Tell

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CFLBob
Registered User


Reged: Wed
Posts: 2
Loc: Melbourne, FL 28.20N 80.60W
General Hurricane Question
      #99100 - Wed Oct 11 2017 08:33 AM

Hi,

This has been my favorite hurricane site for several years, but I've never registered until now. Just made use of all the great information. Now I've got hurricane question that's bugging me enough to want to ask an expert.

Hurricane Nate a few weeks ago got me thinking about something I picked up in the past. According to NOAA, when winds are cited, they already include the forward motion of the storm. ( NOAA Page by Chris Landsea himself! ) First off, when the Weather Dude on TV says to add the forward motion to the winds, you don't need to - they already did.

Second - that means that when you look at a storm like Nate, with 85 mph winds and a forward motion of 20, the only place where hurricane winds exist is on the right side of the eye, probably only in the eyewall. On the west side of the storm, the winds were 45, because vectors. On the north and south sides of the eye, the winds are 65. It almost seems that Nate shouldn't be called a hurricane because the only thing making it a hurricane is the forward speed. If Nate were stationary, it would have been a 65 mph tropical storm.

How long have winds been stated this way? It seems to me it wasn't this way years ago.

One of my earliest memories in life was Hurricane Donna in Miami. Living in Miami, then up the east coast of Florida all my life, I've been through a bunch of storms. There has always been a bunch of hype about the storms, but it just seems to be increasing.


Bob
Melbourne

--------------------
Retired engineer who still has more hobbies and interests than time.


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cieldumortModerator
Moderator


Reged: Mon
Posts: 1635
Loc: Austin, Tx 30.40N 97.80W
Re: General Hurricane Question [Re: CFLBob]
      #99101 - Sat Oct 14 2017 12:03 PM

Quote:

Hurricane Nate a few weeks ago got me thinking about something I picked up in the past. According to NOAA, when winds are cited, they already include the forward motion of the storm. ( NOAA Page by Chris Landsea himself! ) First off, when the Weather Dude on TV says to add the forward motion to the winds, you don't need to - they already did.



This is correct. If the Maximum Sustained Winds as advertised by NHC are "x," there is no need to add forward speed to "x." It is already included one way or another.

Quote:

Second - that means that when you look at a storm like Nate, with 85 mph winds and a forward motion of 20, the only place where hurricane winds exist is on the right side of the eye, probably only in the eyewall. On the west side of the storm, the winds were 45, because vectors. On the north and south sides of the eye, the winds are 65. It almost seems that Nate shouldn't be called a hurricane because the only thing making it a hurricane is the forward speed. If Nate were stationary, it would have been a 65 mph tropical storm.




As Chris Landsea notes, the above formula is generally, 'typically, ' the case, but not always.

If a forward speed of a given cyclone is, for consideration's sake, 20 MPH, with max sustained winds of 85, there is no guarantee that the winds would have been 'only' 65 otherwise, and it could even be overly assumptive to then (subtract) yet another 20 from the left semicircle from the 'would have been' winds. The forward speed addition is not an exact science by any stretch - best used as an approximation that does not apply to every situation. Another reason recon, radar, scatterometter, buoys, etc. are all such critical players in forecasting - even nowcasting.

Quote:

How long have winds been stated this way? It seems to me it wasn't this way years ago.





It's more or less always been this way, as far as I am aware. If max winds were found to be 85 MPH a century ago, they were recorded as 85 MPH. No adjustment to 'net out' forward speed was made then, or now.

Keep in mind that the Saffir-Simpson Scale is a wind scale, not an intensity scale.

In 2017 for example, the most intense hurricane so far has been Maria, at 908 hPa, despite having max sustained winds listed 10 mph less than Irma, whose minimum central pressure was 914 hPa.

Saffir-Simpson scale is usefull, but is limited. It is *only* a wind scale, and a very myopic one at that.


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CFLBob
Registered User


Reged: Wed
Posts: 2
Loc: Melbourne, FL 28.20N 80.60W
Re: General Hurricane Question [Re: cieldumort]
      #99111 - Sun Oct 15 2017 12:07 PM



Thanks for the time and effort to reply. I just can't visualize how the winds would not add the way I think, but that means an opportunity to learn.

--------------------
Retired engineer who still has more hobbies and interests than time.


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cieldumortModerator
Moderator


Reged: Mon
Posts: 1635
Loc: Austin, Tx 30.40N 97.80W
Re: General Hurricane Question [Re: CFLBob]
      #99112 - Sun Oct 15 2017 12:19 PM

Yw. So very many other factors at work. For example, one of the more frequent (other) reasons the left semicircle comes in weaker is due to dry air entrainment ... (as seen with Nate) .. preventing the strong winds aloft from efficiently transporting down to the surface (perhaps except in some microbursts).

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