No, it's not a bug. Matlab datenumbers are defined as days since Jan 0, 0000. But if you look at the attributes for your time variable:
>> ncdisp(url, 'time')
Source:
http://nomads.ncep.noaa.gov:9090/dods/wave/wna/wna20150804/wna20150804_00z
Format:
classic
Dimensions:
time = 61
Variables:
time
Size: 61x1
Dimensions: time
Datatype: double
Attributes:
grads_dim = 't'
grads_mapping = 'linear'
grads_size = '61'
grads_min = '00z04aug2015'
grads_step = '3hr'
units = 'days since 1-1-1 00:00:0.0'
long_name = 'time'
minimum = '00z04aug2015'
maximum = '12z11aug2015'
resolution = 0.125
you'll see that the reference time for that variable is Jan 1, 0001. So the proper conversion is
t = ncread(url, 'time') + datenum(1,1,1);
datestr(t([1 end]))
ans =
06-Aug-2015 00:00:00
13-Aug-2015 12:00:00
(Though there seems to be a 2-day shift in there... if this is model data based on a 365-day year or something like that, then datenumbers may not be the best thing to use).
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