The rainiest months in Jamaica are normally May-June and September-October (lasts until November sometimes). This so-called rainy season is characterized by brief afternoon showers followed by sunshine. Look at it as a welcome break from the tropical heat.
Now, if there’s a tropical storm or hurricane activity.. it’s a totally different story.. it will be non stop rain. Hurricane season starts mid June and lasts until mid November, with it’s worst activity between Aug-Oct.
Hope this helps!