The Weather Gauge is an item that works similarly to the Treasure Gauge, but you can only view it on the World Map. When you hover above an area, check where the needle on the dial above the area picture is located. The farther to the left in the yellow zone it is, the higher chance that you'll have a hot day. The farther to the right in the blue zone it is, the higher chance that you'll have a stormy day. If it is not as intense in either zone, then the day will just be sunny, rainy, or if it is in the grey area in the middle, misty.