It's pronounced "YAH-veh" not "YAH-weh." Waw in my opinion should be called vav since there's no "w" sound in Hebrew. Some people refer to it as such since that's how it's pronounced.
As in any language, there have been changes in the pronunciation of Hebrew. Modern Hebrew doesn't have the w sound, but Ancient Hebrew is believed to have had it. See "Reconstructing the Pronunciation of Biblical Hebrew, A simplified Guide to the Main Points" by David Steinberg (http://www.houseofdavid.ca/anc_heb.htm).