Tsunami warnings in Hawaii are broadcast by the Pacific Tsunami Warning Center and through NOAA's weather broadcast. The PTWC is based in Ewa, so technically it's kama'aina. I live on Oahu right now and I've never received a tsunami warning with Google Now, only with the Wireless Emergency Alerts (WEA) that are not specific to any carrier or phone. Flood and severe storm warnings are also broadcast using the WEA.