If an arriving aircraft reports experiencing a 25-knot loss of airspeed and a severe microburst on short final approach, what must the Tower controller immediately do?

1. Immediately broadcast an urgent windshear warning with details to all approaching and departing aircraft, inform airport meteorological services, and record the Pilot Report (PIREP).
2. Keep the report confidential to prevent passenger panic.
3. Instruct the next landing aircraft to land at maximum speed without warning.
4. Close the control tower and leave the facility.