Jupiter has an axial tilt of about 3 degrees so if the dark spot is not midway between the top and bottom of Jupiter it's not on the Equator. I measure it at about 30S you can try it yourself with a ruler. Galileo impacted at 1/4 of a degree south of the equator which is a long way from the dark spot. The banks of color indicate that parts of the clouds don't move up and down but stay at the same latitude. If not you wouldn't see bands like this. So I can't see how the probe would travel that far, and that's an enormous distance. I think you'll find the probe was also orbiting in the ecliptic so there wouldn't be any residual momentum moving it south.
I did quite a bit of enquiring at sci.physics on this and there seems to be no chance Hoagland is correct. Plu-238 is not fissile meaning it can't explode. A small amount of it may if you put it with Plu-239 but that's because the neutrons from the Plu-239 impact the Plu-238. In the probe there are no neutrons to activate the Plu-238. Even if there were there would only be a tiny amount of it exploding. It doesn't matter about the temperature and pressure on Jupiter because in an A bomb they are much greater and they don't make the Plu-238 explode there even with neutrons. Hoagland got it worng on his Plu-238 bomb because that wasn't what it was, only a small part was Plu-238 and it was the Plu-239 that made the explosion.
Also when comets impact they make far more pressure than this bomb would have yet they never initiate fusion on Jupiter. The reason is it's not how fusion works, there must be a compression and confinement and deuterium is not common enough. It's a bit like melting a candle and putting it in your gas tank, candle wax burns and is runny sometimes like petrol but you can't run a car engine on it. Plu-238 is a bit like an A bomb but it's not, and a hydrogen bomb is a bit like Plu-238 in a hydrogen atmosphere except it's not close enough for anything to happen. Frankly I see no possibility that any combination of circumstances could make an explosion out of Galileo. I thought there might be, I asked the experts and it's wrong. End of story and another Hoagland fantasy. Even Steadman said it was really remote as a possibility. If you don't accept it go to sci.physics and ask.