Answer:
is going
Step-by-step explanation:
Don't forget to take your umbrella it is going to rain by the time you got to school.
Is going is a 'future continuous tense.
'To refer to the future in English, there are various different tenses that might be utilized. Will and going to are the two most frequent verbs. These two words are frequently, and especially in informal conversation, used interchangeably without any problems. They do, however, differ slightly when writing in a formal setting. You should be aware that will is more frequently utilized with recent decisions, specific futures, and predictions if you want to be as accurate as you can. Going to is frequently used in reference to predetermined events.
Going to is a future tense verb that refers to an event that has already been scheduled.
Example: Last week they decided that they are going to travel with friends.
Going to is also used when there is current information indicating that something will occur.
Example: You are going to fail if you do not study hard.
Therefore, Don't forget to take your umbrella it is going to rain by the time you got to school.