It is known that there are severe heat-island effects in the urbanized area such as Taipei and that temperature increases are causing hydrological change. The city continues to develop, so it is urgent that the region creates early warning methods. In this study, we observed the influence of the heat-island effect on temperature, precipitable water vapor (PWV) and rainfall in a suburb in Taipei and confirmed that the urban area had a rising temperature trend during the period from 2006 to 2014, approximately 0.7 degrees higher than that in the suburb, which decreased by 1.1 degrees. The average PWV increased by approximately 6.7 mm and the cumulative rainfall increased approximately 54.7 mm. Two other high-temperature areas are in the development zone and in the northern mountainous area, which is lower in temperature, and a heat-island effect is obvious. Rainfall is greatest in the southern mountainous areas in summer. Due to wind direction in the winter, rain falls in the northeastern region of the windward side. Our results also show that there is a significant urban heat-island effect in the Taipei region and that PWV and rainfall are increasing in the urban area with global warming.