Re: Reminder that NHC won't use line in graphics this year, just the cone.
Posted by Chris in Tampa on 6/6/2009, 10:03 am
The NHC releases points at forecast times that start off every 6 hours, then every 12 hours and finally to every 24 hours on the last days of a five day forecast.

Computers across the world access that data and plot those coordinates so that television outlets can plot it on their weather systems for broadcast, images can be created for the internet, and ships can write down the coordinates and plot it themselves on a map.

While the NHC could try and curve the line to where they think the storm will likely travel, for others to do the same the NHC would have to actually release a product that could tell other computer systems how it should be drawn. For people simply taking the coordinates down on a ship, that would not be practical. That means they would still have to make a note in the discussion, like they normally do when the storm is near land and expected to make some kind of sharp curve, that the storm might get closer to a coast than two forecast points show since the storm will curve further before it curves back to the other forecast point. That information would still have to be relayed by those means so that people who could not plot the curve could still understand that easily.

The NHC also gets data from models at intervals that do not contain every moment in time. The NHC would have to make an educated guess beyond the forecast points to approximate a curve. They might not be ready to be so specific about a curve. Perhaps when models generate more frames, like every half hour or hour and with better data, then they could be more precise and provide a curve to the public.

The circles the NHC generates are already a curve:
"The cone represents the probable track of the center of a tropical cyclone, and is formed by enclosing the area swept out by a set of circles (not shown) along the forecast track (at 12, 24, 36 hours, etc)."

As it is, those sweeping circles would not be exactly replicated by computer programs that display the cone. So if the NHC did that to the line in their graphics, no one else would get the info unless they specifically release a text product for other computer systems to do that.
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Reminder that NHC won't use line in graphics this year, just the cone. - jack ruby, 6/2/2009, 5:09 pm
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