The most common and most likely answer to this crossword clue is the 9 letter word TEMPORARY
I've seen this crossword clue in The Daily Telegraph
T
E
M
P
O
R
A
R
Y
More clues leading to the result TEMPORARY
- Sorrowful about politician and other men as fly-by-nights?
- Fleeting romp turned into weeping
- Portray me looking unconventional, casual
- Momentary crying about politician getting nothing right
- Provisional speed on approximately 28 per cent of railway lines
- Portray me being silly — here today, gone tomorrow
- Stand-in soldiers on railway follow recommended speed
- Brief time, special, cut short before the end of holiday
- Acting sad when describing prom gone wrong
- Irregular pace seen by soldiers near the line
Buddy explains!

The straight part
We know that "here today, gone tomorrow" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case here today, gone tomorrow = temporary.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TEMPORARY mean?
TEMPORARY noun- One serving for a limited time; short-term employee.
- Not permanent; existing only for a period or periods of time.
- Existing only for a short time or short times; transient, ephemeral.