To take an immediate measurement, you must keep the air moving around the temperature sensor. If there is a strong breeze, just point the Kestrel into the wind. If there is no wind, swing the Kestrel around in a circle on its lanyard or rapidly wave it back and forth in hand. This ensures that the sensor measures the temperature of the air rather than the temperature of the case.
Alternatively, if you have time, allow the Kestrel to rest where you want to measure the air temperature (NOT in your hand) until the case temperature equalizes with the air temperature. When equalized, the display will read a constant value. Be aware that this could take as long as twenty minutes.