Using Deep Learning to Nowcast the Spatial Coverage of Convection from Himawari-8 Satellite Data

Predicting the timing and location of thunderstorms ("convection'') allows for preventive actions that can save both lives and property. We have applied U-nets, a deep-learning-based type of neural network, to forecast convection on a grid at lead times up to 120 min. The goal is to make skillful forecasts with only present and past satellite data as predictors. Specifically, predictors are multispectral brightness-temperature images from the Himawari-8 satellite, while targets (ground truth) are provided by weather radars in Taiwan. U-nets are becoming popular in atmospheric science due to their advantages for gridded prediction. Furthermore, we use three novel approaches to advance U-nets in atmospheric science. First, we compare three architectures-vanilla, temporal, and U-net++-and find that vanilla U-nets are best for this task. Second, we train U-nets with the fractions skill score, which is spatially aware, as the loss function. Third, because we do not have adequate ground truth over the full Himawari-8 domain, we train the U-nets with small radar-centered patches, then apply trained U-nets to the full domain. Also, we find that the best predictions are given by U-nets trained with satellite data from multiple lag times, not only the present. We evaluate U-nets in detail-by time of day, month, and geographic location-and compare them to persistence models. The U-nets outperform persistence at lead times >= 60 min, and at all lead times the U-nets provide a more realistic climatology than persistence. Our code is available publicly.