PlanetsCentral

Initial_voltage =
    5 + Random(Trunc(Number_of_ships_in_game) / 5)
    ...that is, stronger storms later in the game
Initial_radius =
    10 + Random(190)
    ...that is, 10 to 200

The initial speed is chosen according to regular movement rules.

The initial location depends on the setting of AllowWraparoundMap.

Wraparound enabled

With wraparound enabled, storms appear at a random place, with random heading.

Wraparound disabled

With wraparound disabled, storms appear in the outer regions of the map, moving roughly inwards.

First, PHost picks an Angle (0..360 degrees) and a Distance (500..1200).

Initial_X =
    Round(Center_X + Sin(Angle)*Distance*Size_X/2000)
Initial_Y =
    Round(Center_Y + Sin(Angle)*Distance*Size_Y/2000)
Initial_heading =
    Angle + 140 + Random(81)
    ...that is, towards the galaxy center, but at most 40 degrees
       to the left or right

The Center_X/Y and Size_X/Y are center and size of the universe, and are derived from WraparoundRectangle. That parameter should therefore still be set, even when wraparound is not used.

With the default WraparoundRectangle of 1000,1000,3000,3000, ion storms will appear within a distance of 500..1200 from the galaxy center. This is the same as with HOST. For larger, smaller, or non-square universes, the formula will adjust the distance accordingly.