Hi there
I am a bit the opposite though -- i find in warmer weather my insulin needs actually increase -- but many
people on the forum report that their needs decrease during warmer weather.
Have you either spoken with your DSN about making adjustments or have you ever looked at doing some basal testing to see how much if any your back ground might be adjusted.
here is a link to basal testing http://www.salforddiabetescare.co.uk/index2.php?nav_id=1007
it is aimed at people on a pump but the principles are the same for people on MDI.
Not mental but do have to make more insulin adjustments to prevent hypo's (mainly when active), but basal requirements do reduce in the warm weather and increase again when it gets cooler.
Edit to add, agree with @himtoo that your basal insulin likely needs reduced if your experiencing regular nigh-time hypo's @rachy0121