SQL row filtering

Hello,

I've been working on this problem in vain for several days now.  I
essentially am looking for one row per hour where that row is the youngest
row of that hour.

So if there are say three rows labeled (17:00, 17:41, 17:43) I only want
17:43's row to show for the 17th hour.  Essentially I want to see what I
have in the table below but just with out the red rows (if you cant see the
red, its the 17:00 and 17:41 rows).  How can I fix or rewrite this select
statement to get what I want.

I've looked at using group by/having, correlated subselects, between.  I can
get a union of 24 correlated subselects to work, but its way too slow for
what I'd need.

Thanks inadvance for any help anyone can give.

- SQL Man

-----------------------------------------------------

SELECT hourlycounter, extract(hour from utcissuetime) as hour,
extract(minute from utcissuetime) as minute, CumulativePrecipitation,
OneHourPrecipitation

FROM observations, awos
WHERE stationid='YIO'
             and hourlyidentifier = 201
             and utcissuedate = '20031006'
             and utcissuetime >= '00:00:00'
             and utcissuetime <= '19:00:00'
             and observations.obsid = awos.obsid
ORDER BY hour DESC, minute DESC;

   hourlycounter | hour | minute | cumulativeprecipitation |
onehourprecipitation
  ---------------+------+--------+-------------------------+----------------
------ 
               0 |   19 |      0 |                    46.5 |
0.5
               0 |   18 |      0 |                      46 |
0.5
               3 |   17 |     43 |                      78 |
               2 |   17 |     41 |                      78 |
               0 |   17 |      0 |                    45.5 |
0.5
               0 |   16 |      0 |                      45 |
0
               0 |   15 |      0 |                      45 |
0.5
               0 |   14 |      0 |                    44.5 |
0
               0 |   13 |      0 |                    44.5 |
0
               0 |   12 |      0 |                    44.5 |
0
               0 |   11 |      0 |                    44.5 |
0.5
               0 |   10 |      0 |                      44 |
0.5
               0 |    9 |      0 |                    43.5 |
0
               0 |    8 |      0 |                    43.5 |
0
               0 |    7 |      0 |                    43.5 |
0
               0 |    6 |      0 |                    43.5 |
0
               0 |    5 |      0 |                    43.5 |
0
               0 |    4 |      0 |                    43.5 |
0
               0 |    3 |      0 |                    43.5 |
0
               0 |    2 |      0 |                    43.5 |
0
               0 |    1 |      0 |                    43.5 |
0
               0 |    0 |      0 |                    43.5 |
0
  (22 rows)