Isohyets

Giambelluca, T.W., Q. Chen, A.G. Frazier, J.P. Price, Y.-L. Chen, P.-S. Chu, J.K. Eischeid, and D.M. Delparte, 2012: Online Rainfall Atlas of Hawai‘i. Bull. Amer. Meteor. Soc., doi: 10.1175/BAMS-D-11-00228.1.
http://rainfall.geography.hawaii.edu/downloads.html
The lines on this map are called isohyets. They are used as a means of specifically showing rainfall and their lineage connects areas of like data for precipitation. The average rainfall in October 2011 for Kaua'i as shown here seems to depend on distance from the center of the island, where the outer edges recieved around 100 mm of rain while the middle received around 600 mm of rain.