The most flights from MEX to HAV are scheduled on a Monday (1 on average). You will have fewer flight options on Monday, which is when the least amount of flights are scheduled (1 on average).
In terms of precipitation, rainfall in Havana ranges from 1.6 - 6.7 inches per month. October is typically the wettest month, when rainfall can reach 6.7 in. March is typically the driest time to visit Havana when rainfall is around 1.6 in.
If weather is an important factor for your trip to Havana, use this chart to help with planning. For those seeking warmer temperatures, June is the ideal time of year to visit, when temperatures reach an average of 80.6 F. Travelers looking to avoid the cold should look outside of January, when temperatures are typically at their lowest (around 71.6 F).