Weather Forecasting

We have seen that the Polynesians had some really nifty tools to navigate, such as the Hawaiian star compass and the latitude hook. Equally interesting to note is how these people used celestial bodies and terrestrial signs to predict the weather.

Celestial Bodies

Islanders of the Pacific thought that an aura or a halo around the moon suggested impending rain. There is some science behind this. The halo could have been due to the moonlight penetrating layers of ice crystals in clouds saturated with water vapour. A halo with small diameter suggested that rain was falling some distance away from their position at the time of observation. A halo of larger diameter meant rain falling nearby. Navigators in the Gilbert Islands even counted the stars in the halo: a number greater than 10 signified moderate rain; a number less than 10 implied heavy rain with strong gusts of wind. If two halos were observed, with the inner one having a reddish-brown appearance, then a terrible storm was thought to be brewing.

Generally, shining stars that blinked were seen as symbols of inclement weather. For example, if the little star (we believe it's Alcor, the optical double star of Mizar) near the Big Dipper winked frequently, they knew a storm was approaching.

Another belief was related to the dark side of the moon. When visible, the air in the direction of the moon was thought of as good and clear.

Sky Color

Red sky during dawn or dust indicated humidity. For example, if the weather was coming from the east and there was red sky at dawn, bad weather could be coming.

References
1. Polynesian Voyaging Society: Hawaiians as Navigators and Seamen
2. Polynesian Voyaging Society: Non-Instrument Weather Forecasting