pentad time series

[N Jyothi]

Hello everyone
          I have a data file, varying in longitude, latitude and time,
with which I need to plot a latitude-time cross-section as:

(1) first average the data between 80 to 100 degree longitude
(2) then create a pentad time series data of the 365 days and plot from 0
to 30 degree latitude (in the final dataset, the time will vary from 1 to
73 (365/5)).

I was trying in the following manner, but it is getting wrong all the way.
The dimension X varies from 1 to 512, Y from 1 to 256 and time from 1 to
365.

'open data.ctl'
t=3
'set y 129 172'
while(t<=10)
'define longave=(ave(precip,x=120,x=150))'
'd tloop(ave(longave,t-2,t+2))'
'set t 't+5
endwhile
.................

The above does not provide any solution, as I need to have a variable in
which the first time value will be average of first five time values
(t=1,t=5), next time value will be average of the next five time values
(t=6 to t=10) and final time value, which should be around 73, should have
time averaged data from t=361 to t=365).

I will be grateful for any help with this.

Regards - Jyothi