I agree with @Gustavson.
"Si esta noche haya mucho lluvia y este muy tormentosa, vamos a ver 'Lost Highway.'
"Esté muy tormentosa" is a somewhat literary you find in writing something like that and I wouldn't translate "there is" as "haya" here, as already mentioned above. If you mean "haya" you’ll need to recast the sentence.
- "Aunque haya (subjunctive present) un temporal, igual(de igual forma) vamos a ver 'Lost Highway"(Even if there is...we will..)
- "Aunque llueva (subjunctive present) o truene(subjunctive present), (igual) vamos a ver 'Lost Highway"
- "Aún cuando llueva o truene (singular 3rd person subjunctive present), (igual) vamos a ver 'Lost Highway"
But "even if" has a different meaning here. We will watch a movie, no matter what the circumstances.
"If there is rain tonight and it's very stormy, we will watch 'Lost Highway.'
In a colloquial way I would say:
- "Si hay temporal, vamos a ver una película" (someone's talking about their plans)
- "Si hay temporal, vemos [indicative present] una película mejor" (the present has future value in this context, using the word "mejor" makes this sound more like a suggestion than a command, it's better if we stay here, if it rains, the best plan is/it's better if you dont go out)
- "Si llueve (indicative present singular 3rd person), veremos [indicative future] una película" (thinking in advance what you are going to do)
- "Si llueve y hay mucho viento mejor nos quedamos (indicative present) viendo una película, ¿Qué les parece?"(= If it rains, we'll just stay inside and watch... what do you think?) (It's just a suggestion)
- En el caso de que llueva (subjunctive), lo que podríamos[indicative conditional] hacer es ver una película (it is a possible scenario)
If the weather forecast says it will be cloudy with a slight chance of rain, then we would say:
- Si se diera el caso de que llueva/Si lloviera|lloviese/Si llegara|llegase a llover, entonces mejor vemos/veríamos [indicative conditional]/veremos una película/lo que seguramente haríamos [indicative conditional]/haremos sería [Indicative conditional]/es ver una película (that is what we would do in that situation if this happens)
IF CLAUSES THAT REQUIRE SUBJUNCTIVE FORM -> Hypothetical situations in the future or the present that are contrary to fact or very unlikely: Si+imperfect subjunctive+the conditional, e.g: Si llueve/lloviera [subjunctive imperfect], no saldré/saldría [Indicative conditional] (if it were to rain, I wouldn't go out)
Si (If) is very rarely followed by the present subjunctive but the rule can be broken -> Especially with negative 'si' clauses (such as - no se si...) the present subjunctive is something to express more doubt, ''si" then takes on the meaning of 'whether' more than 'if'. E.g. No se si estemos (subjunctive present plural 1st person) en casa (I don't know whether we'll be at home)