The upper ocean temperature and dynamic height fields are correlated in the western North Pacific Ocean. This relationship can be used to map a relative geostrophic stream function of the Kuroshio Extension using temperature data from expendable bathythermograph (XBT) surveys. We have examined the ability of the North Pacific ship of Opportunity XBT program, known as TRANSPAC, to carry out this procedure. Estimates of 600/1200 dbar geostrophic shear were generated from the XBT data utilizing objective mapping techniques. These estimates were compared with measured currents at 600 m relative to 1200 m along 152 ¿E from 27 ¿N to 42 ¿N. The estimated and measured relative currents are positively correlated, with an rms error of ¿6 cm/s over a measured dynamic range of 30 cm/s. However, the XBT estimated shears consistently underestimate the measured values by a factor of 2 to 3. The underestimate of the amplitude is the result of both undersampling and mapping procedures that eliminate high wavenumber contributions of the dynamic height variability. These factors appear to be responsible for previous differences in amplitude between directly measured and TRANSPAC XBT extimated values of relative eddy kinetic energy and Reynolds stress. The TRANSPAC XBT survey can only monitor qualitatively the dynamic topography of the Kuroshio Extension meanders and rings. The variability outside of the extension with a temperature range of 3 ¿C cannot be resolved because of inaccuracies in the temperature-dynamic height relationship. To monitor the Kuroshio Extension variability in the future, it is recommended that TRANSPAC XBT resources in the western North Pacific concentrate on obtained a denser sample of the field during the fall and winter seasons because of incomplete ship track coverage in spring and summer.