Like rainiest day, month, season, or year and dryest day, month, season, or year? I would think a for loop and/or the sum(), min(), max(), median(), std() and mean() functions would come in useful, assuming your data has already been imported into an array in MATLAB. If not, try readtable(), csvread(), importdata(), dlmread(), and lots of other functions for reading in data. For example if you have a 365 row (day) by 95 column (year) array, then the wettest January:
allJanuaryDays = array(1:31,:); % Rainfall from every January date for every year.
monthlySums = sum(allJanuaryDays, 1); % Sum over days
[wettestSum, indexOfWettestYear] = max(monthlySums);
And if you have the ability to accurately predict rainfall from today through the year 2100, please come to work in our town!