SensorPush sensors will perform quite well outdoors, provided they are protected from direct sunlight and precipitation.
While we don't call them waterproof since they are not intended to be submersible, the HT.w and HTP.xw devices are water-resistant with o-ring seals and protective sensor membranes and are much more robust in tough applications, and as such are the devices of choice for the outdoors.
However, many users have had good results with the HT1 hanging under the eave of a roof or in other similarly protected outdoor conditions. Since the HT1 has an open sensor hole, it's also a good idea to mount the sensor with this hole facing downward to lessen the likelihood of water or debris getting inside.
You will also want to protect your sensor, regardless of model, from direct sunlight. Solar radiation isn't particularly harmful to the device, but it will heat the case and skew the temperature and humidity readings. For optimal accuracy, you'll want a mounting location that protects the sensor from direct sunlight as well as precipitation, but that also offers good airflow so it's able to get an accurate representation of the ambient environment. We've found that under an eave generally works quite well, but there are also specifically designed solar radiation shields available for such an application.