According to the earlier linked stories, OBL figured that one out and has bypassed that threat level and gone directly to attempting to manufacture military-yield weapons in the 10-15kt range, roughly equivalent to the Hiroshima bomb (hence the project name). The reference to Hiroshima is propagandistic and intended to reflect the onus back on the U.S. Government, for having used those weapons during World War II.
Practical effects of a 10-kt weapon, if detonated at some optimum height above ground (say, atop a big building): basically nonsurvivable within about 1.2 miles, massive destruction and relatively low survivability (~25% survive at least into the postattack period) out to about 2 miles. Blast wave velocities over 250 mph instantaneous close to Ground Zero.
At 2 miles, most buildings remain standing and occupants not located next to windows will probably survive if they leave the area immediately and don't get caught in firestorms and aren't irradiated heavily by fallout. Persons near windows will be burned and then cut by flying glass; blast wave velocity will be approximately 70mph.
Over four miles, minimal effects on persons indoors except for fallout. Light damage to buildings and vehicles. And pandemonium, civil disorder, loss of services, etc.
There will be other effects, such as immobilization of vehicles with computerized ignitions by EMP and destruction of computer equipment by same. I've no idea about ranges and severity of EMP effects.
Search the Net for "weapons effects" and some combination of keywords.
Oh, yeah.
Last I heard, he'd rounded up a task force of goatherds and they were going to build a Trident submarine with 240 independently-targetable warheads.
Now we're really screwed!