| cieldumort |
| (Moderator) |
| Sat Oct 14 2017 12:03 PM |
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Re: General Hurricane Question
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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.
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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.