I once wrote to a friend:
Greetings [name deleted],
It seems like what we have in 1 Thess 4:17 is another rhetorical device, namely, pleonasm (PLEONASMOS). Pleonastic speech is basically another way of describing redundancy. While redundancy normally gets a bad rap, linguists have shown that it is a normal part of human speech. At any rate, David A. Black defines pleonasm as "the use of more words than necessary, as in 'He was appointed temporarily, for the time being.' Pleonasm is evident in such redundant language as hUMAS . . . hUMAS in Colossians 2:13 and MALLON KREISSON ('more better') in Philippians 1:23"(Linguistics for Students of NT Greek, page 136).
Under the entry for hAMA in BDAG, we also read:
"Apparently pleonastic w[ith] SUN (cp. Alex. Aphr., An. 83, 19 hA. AISQOMENH SUN AUTWi; En. 9:7; Jos., Ant. 4, 309; cp. SIG 705, 57 hAMA MET AUTWN) to denote what belongs together in time and place (about like the Latin UNA CUM): hA. SUN AUTOIS hARPAGHSOMEQA 1 Th 4:17. hA. SUN AUTWi ZHSWMEN 5:10."
The Latin UNA CUM means "together with."
1 Thess 5:10 seems to be a clear example of hAMA being employed pleonastically with SUN. It is even more stark there than the same phrase found at 1 Thess 4:17.
David J. Williams (1 and 2 Thessalonians) adds that the whole phrase hAMA SUN "is emphasized by placing it early in the sentence before the verb" hARPAGHSOMEQA
(Williams, page 85).
Williams also notes that hAMA "reinforces" SUN here.