Warning of real disaster starting tomorrow? (5)
I believe the answer is:
alert
'warning' is the definition.
(alert is a kind of warning)
'real disaster starting tomorrow?' is the wordplay.
'disaster' is an anagram indicator.
'starting' says to take the initial letters.
The first letter of 'tomorrow' is 't'.
'real' is an anagram of 'aler'.
'aler'+'t'='ALERT'
'of' is the link.
(Other definitions for alert that I've seen before include "Vigilantly attentive" , "In state of watchfulness" , "Signal danger" , "Wakeful, observant" , "Wide awake and watchful" .)