Ho yeah... you'll be sweatin' like a pig! Hopefully they'll let you do some gi-less training too. One problem I find w/ gi grappling (aside from the immense discomfort) is that people become too reliant on grappling the baggy gi itself, which is not incredibly practical for modern day self defence where most people don't walk around in their pyjamas. Good grappling should be focused purely on grabbing the body, not the clothes (no chance for clothes cheating in traditional Greek wrestling! )

Does your Jujutsu school use a "closed" Ukemi or "Open" Ukemi, or the more open version? I find the open version is more commonly practised, but leaves you horribly exposed.
Open Ukemi = exposed ---> <--- Closed Ukemi = better defended