Wet bulb reading higher than dry bulb
This can happen only under the following circumstances:
i) Insufficient evaporation taking place from the wet bulb due to dust, salt or other impurities on the muslin, or due to no water on the muslin.
(ii) Insufficient time interval allowed after shifting of Stevenson’s screen to windward, addition of distilled water, renewal of wick or water, etc.
(iii) Difference in the sensitivity of the thermometers whereby one of them is slow in recording sudden changes of temperature
(iv) Faulty or broken thermometers.
Ref: Marine Meteorology by Capt H Subramanian
