They also changed it from "radiation" to "electromagnetic radiation" for some reason on another report of radiation, but I'm just being schizo here
I believe it's primarily high powered radar testing, I'm sure they do other stuff there but if you look in the general direction north and west of the island you'll see what they could be monitoring with radar.
Here's the current interesting NOTAMS(Notices to Airmen) for PKWA
M0148/25 - RWY 24 PRIOR APPROVAL REQUIRED FOR TAKEOFF DEPARTURES DUE TO
ELECTOMAGNETIC RADIATION HAZARD. 30 MAY 17:54 2025 UNTIL 30 JUL 23:59 2025.
CREATED: 30 MAY 17:54 2025
M0147/25 - CONTACT TOWER/BASE OPS MINIMUM 50NM OF BUCHOLZ AAF AND PRIOR TO
DEPARTURE FOR ELECTROMAGNETIC RADIATION HAZARD DECONFLICTION. 30 MAY 17:53
2025 UNTIL 30 JUL 23:59 2025. CREATED: 30 MAY 17:53 2025
M0141/25 - ALL ARRIVALS AND DEPARTURES MAKE SOUTH TRAFFIC ONLY TO AVOID
ELECTROMAGNETIC RADIATION HAZARDS. OVERFLIGHT OF THE ISLAND NORTH
OF RWY IS PROHIBITED. 30 MAY 17:47 2025 UNTIL 30 JUL 23:59 2025. CREATED: 30
MAY 17:47 2025
My guess is these are really continuous they just issue them 60 days at a time for some reason.