mpirun retaining redirected stdout

I am running in a cluster. I tried to run my executable with 4 different forms:

In serial, with
```
myexec
```
This starts giving output in stdout right away, as expected.
In serial, redirecting stdout and stderr, with
```
myexec > out-err.log 2>&1
```
This starts giving output in out-err.log right away, as expected (verified with cat out-err.log in another terminal).
In parallel, with
```
mpirun -n 2 myexec
```
This starts giving output in stdout right away, as expected.
In parallel, redirecting stdout and stderr, with
```
mpirun -n 2 myexec > out-err.log 2>&1
```
This retains output until job is finished (due to completion or time allowance).

Is there any way of having stdout/stderr "flushed" at runtime in case 4, so I can check out-err.log?