1 He will not leave if it isn't fine tomorrow. 2T

1 He will not leave if it isn't fine tomorrow. 2T

第一句中的fine是形容词，it is fine是主系表结构，边否定句直接在is后加not就可以了；
第二句中的rain是实义动词，it rains.是主谓结构,变否定句要借助助动词does.

类似第二句，边否定句或疑问句要借助助动词的动词有:
实义动词
系动词中的表感官或（不）变化的词:feel, sound, get, become...
还有情态动词中的have to, used to

估计你对动词的分类不是很清楚，特附上：

一、行为动词/实义动词
及物动词
不及物动词

二、（连）系动词
be
taste, feel, look, seem, sound…
turn, become, get，grow, stay, remain…

三、助动词
be (been, being, am, is, are, was, were)
do (does, did)
have(has, had)
will, would, shall, should

四、情态（助）动词
can, could
may, might
must,have to
will, would
shall, should
used to, ought to
need, dare

他还没决定是否明天动身去北京。