Katrina is a fortune teller cat who may appear in a tent in your plaza during the week. She can give you a reading and tell you how your luck will be today. She can also recommend a lucky item to wear that will boost your luck during the day. If you get enough readings for her, you can build a fortune teller shop in Main Street for her to move into permanently.
Katrina is a Special Visitor who can appear in a tent in your town plaza up to once a week, Monday through Saturday. She is not guaranteed to show up every week. If she is in town, her tent will be open from 9AM to 7PM.
You can get a reading from Katrina for 500 bells. She will tell you about your luck for the day. She will recommend a specific type of item to wear for good luck. If you wear that item, your luck will be increased until 11PM.
To unlock the fortune teller shop, you or any other residents of your town need to have Katrina tell your fortune 20 times. You can even go to other towns and visit Katrina there. This helps increase your fortune count more quickly since Katrina will only show up in your town up to once a week.
After the 20th fortune that she tells you (or anyone from your town), she will stop you when you try to leave and will suggest building a public works project for her. The mayor of your town can then sit in the mayor chair in your town hall and choose the Fortune Teller's Shop from the list of public works projects to build.
For more details, check the Shop Unlock Guide. In the Fortune Teller Shop, Katrina will give you a reading for 500 bells as usual.
After you build the Fortune Teller Shop, Katrina might offer a rare item for 10,000 bells if your item luck for the day is good.
In Animal Crossing: New Leaf, your luck is random every day. To learn more about the different types of luck, please read the luck (or "why do I keep tripping?") page.