long history already that issue
the Tempest is now covered by a special coating that reduces this case but it can happen that during and after a shower droplets stay on the lower plate (gap where the wind is measured). If those are in direct line with the sensors it ‘deforms’ the signal and you get false readings. We saw cases where it drizzled for hours and hardly any wind resulting in those droplets. Sometimes it can happen when it rains hard in diagonal and the plate is soaked … in general the problems disappears as it dries out