Originally Posted by Frenchy
The undertail coverts appear to be too short to be an acrocephalus warbler, and i ca't recall ever seeing a Marsh wagging its tail around. I also think the pale fringes to the secondaries and tertials go dome way to ruling out Olivaceous, although it would be nice to see the tertials and the bird not in shade.
I recieved this message from an UAE birder on the subject
We saw 130 Marsh Warblers in the UAE today and this bird looks fairly similar. However it appears to lack the olive green upperparts and buff-yellow underparts of Marsh and perhaps has a slightly-too-prominent supercilium. I would therefore go with Reed (Eastern / fuscus presumably) but for me the light does make it impossible to say for certain. Rump colour (if noted) would be another clue (should be warm brown in Reed at this time of year but more or less concolorous with mantle in Marsh).
Blyth's Reed is another possibility but it appears to lack the 'flattened head' of that species, and also the dark tip to the lower mandible.