Ryk wrote:
...I interpret 10-15
from the southwest to mean 5 -20 from a direction somewhere between
south and west, so variation is moot. ...

The OP says he has almost two points of variation which is nearly half
of your four points of expected error. Seems to me that the difference
between True and Magnetic is worth considering at least in a general
way in his case.

-- Tom.

wrote:
Ryk wrote:
...I interpret 10-15
from the southwest to mean 5 -20 from a direction somewhere between
south and west, so variation is moot. ...

The OP says he has almost two points of variation which is nearly half
of your four points of expected error. Seems to me that the
difference between True and Magnetic is worth considering at least in
a general way in his case.

-- Tom.

We don't all sail off the coast of Maine, so the variation will depend on
where you sail.

I would think that the reason weathermen use the cardinal points system
rather than actual degrees is that it gives them some leeway in their
estimates of what direction the wind will blow from, since the wind veers
and backs many times an in hour sometimes, as anyone who has raced will
testify.

....
I would think that the reason weathermen use the cardinal points system
rather than actual degrees is that it gives them some leeway in their
estimates of what direction the wind will blow from, ...

Good point. If you are using data from an automatic reporting station
or a digital model then you will get a report in degrees. Of course,
even in the precise area of the station or grid the wind will vary over
time and forecasts all have some level of error as well. WX reports
usually try to predict conditions over time and area which adds more
uncertainty. It all gets pretty fuzzy, pretty quickly.

-- Tom.