Answer:
Missing data points
Explanation:
Given that there are 12 calendar months in a year, and there are clearly defined raining season in some areas which may last for months, following periods of low rainfall or zero precipitation, the sample should include all the months of the year so as to ensure, that the effect that causes rainy season such as the landward direction of moist air from the sea or the seaward of air during periods of dry season.
Other possible causes includes;
Heteroscedasicity
This occurs when the variability of the dependent variable is not constant with regards to the independent variable
Multiple linear regression
The relationship between rainfall and air pressure as well as other factors is a multiple linear regression