I'm looking at the specifications of an ohmite shunt resistor: <http://www.ohmite.com/catalog/pdf/10_series.pdf>

It is a 0.005 ohm resistor, rated at 2,3,5 and 7 Watts (4 different parts in the same datasheet) at 25C ambient. But there is no information about thermal resistance. 

If my current over this resistor is going to be, say 30A, then power dissipated on this resistance is going to be 4.5W. Does this mean that if I pick a 5W or 7W resistor, I will be OK in free air (no cooling requirements)? What if my ambient is *not* 25C? Since there is no thermal data in the datasheet, how can I go about calculating cooling requirements for an ambient temperature of 50C? Are shunt resistors never cooled?