Since there might not be an equal number of wind speeds above and below your threshold, you shouldn't use a matrix (which requires an equal number of rows). Instead, use a cell array.
Here's how to identify rows that have wind speeds between [5,10] and rows that have wind speeds >10.
set1Idx = Podaci(:,2) >= 5 & Podaci(:,2) <= 10; %index of rows that are between [5,10]
set2Idx = Podaci(:,2) > 10; %index of rows that are above 10.
Use those indices as needed. Try to avoid splitting up your data into different variables. Here's an example that averages azimuth according to your groups.
m1 = mean(Podaci(set1Idx,3));
m2 = mean(Podaci(set2Idx,3)):
