I agree. Not to mention that in tropical and equatorial countries there are non-rainy seasons, that depending on the site, run more or less from July to September and December to February or so.
At least where I live you have to avoid some sites (because it rains every evening) in April-June and October-November. So, I would say this is not a very good date for this particular GP.
I wonder how much weight meteorology is given in the calendar, because up to this days, with maybe less asiatic and exotic racetracks, the record of halved races is very good.
One thing is a short rain that makes the race more interesting (remember when people was surprised by changes in position because of the rain?) and another is a torrential downpour in the tropic that perhaps could be avoided more carefully. On the other hand a pit race is always a drama.