Flood is a natural disaster that many occur in Indonesia. Losses caused by the flooding is huge both materially and lives. Therefore, a system is needed that can tell when the floods come and what areas are affected to allow proper evacuation and can inform the possibility of flooding several hours before the floods occur. Flood Forecasting using Holt-Winters Exponential Smoothing Method and Geographic Information System. This forecasting technique helps to know when a flood occurred with past water debit data and with the help of Geographic Information System shows flood-affected areas corresponding to previous year's flooded inundation data. Then with the help of hardware Arduino Uno provides water flow and water level data directly obtained from the water flow sensor and ultrasonic sensor then calculates the possibility of flooding in accordance with the area in the previous year's flooded inundation data and with the help of the database using mysql to display information such as Map of inundation flood, water debit and water level.