I have a 2001 Forester (automatic transmission) and lately have noticed
the following problem.  In the morning, as I first leave the house, the
car shifts fine between 1st and 2nd gears, but from 2nd to 3rd, it's
really harsh.  It kind of stays in 2nd gear a bit too long, then lurches
into 3rd.  3rd to 4th is no problem.  This happens only in the morning.
10 hours later as I leave for home, the weather is a lot warmer, and
there doesn't seem to be a problem -- at least not as pronounced.

Temps in the morning here have been around 65 degrees.  By the later
afternoon, it's around 88-92 degrees (Central Virginia).  The car has a
little over 43,000 miles on it.

Any ideas on what the problem may be, and how to address it?

Thanks!