Widebody Transport
Flight Crew Air Transport Pilot (ATP)
Ground Event / Encounter Other / Unknown
Flight Crew Rejected Takeoff; Flight Crew Returned To Gate
Weather
Normal pushback and start. Prior to taxi; we setup three runway changes in the FMS due to rapidly changing winds. First RWY 33; then RWY 25L; and finally RWY 15. Windshear advisories were not included in the most current ATIS report. Last reported winds were 120/15G26 KT. During takeoff; we received a 'HEADWIND SHEAR' CAWS (Caution and Warning System) alert at 154 KT; which was also our V1 speed. Captain commanded and executed a reject. Airplane easily decelerated to taxi speed with at least 2000 feet remaining. Cleared the runway and taxied back to our departure gate; but kept the engines running while we reviewed rejected takeoff and brake cooling procedures. While in the gate; I advised Operations and coordinated with Maintenance for a tire and brake inspection. After receiving updated fuel burn calculations from Operations and confirmation from Maintenance that our current brake temperature allowed a subsequent takeoff; we pushed back for another attempt. Taxi and subsequent takeoff on RWY 15 were uneventful. Rapidly shifting winds.
Flight Crew flying aircraft encountered Headwind Shear on takeoff roll.