Dave Honess, over at the Foundation, has just announced the availability of a SenseHAT emulator. It allows you to use a virtual SenseHAT and program it with the sense_hat Python library. Pretty neat! You can even manually alter the virtual sensor readings to see it affecting your program. You can access the emulator and see a variety of sample programs over at trinket.io and read a bit more about the development of it over at Raspberry Pi HQ.