Predicting Hurricane Trajectories Using a Recurrent Neural Network
Presented by
Yishu Duan, Xibei Di, Xin Yan
Introduction
Hurricanes originate in the warm water of the Caribbean Sea and Atlantic Ocean, and generally travel from their origin to the north, northwest, or northeast. Hurricanes are usually accompanied by strong winds, heavy rainfall, and dangerous tides, as one of the most common natural disasters on the planet, hurricanes could threaten the safety of people’s economic property assets and human lives. This makes predicting the hurricane paths by modeling the hurricane behavior extremely essential.
Recurrent Neural Networks (RNNs) are a kind of artificial neural networks, where the weights of it can be modified to make the model learn complex dynamic time-dependent behavior. A RNN can effectively simulate the complex nonlinear temporal relationship of hurricanes, which can improve the future prediction of the accuracy of hurricane path.
Thus, in this paper, fully connected recurrent neural networks using a grid model are built for hurricane track prediction, and the result will be compared with other hurricane predicting techniques.
Related Work
Scientists had been advocating in developing models for predicting and tracking hurricane paths, and had been persistently improving the accuracy over the past decades, whereas these currently existing models are quite different from each other in terms of the structure as well as the complexity. The four main types of models currently used by the National Hurricane Center (NHC) of the National Oceanic and Atmospheric Administration (NOAA) include:
- Dynamical models
- Complex since the highest computing power is desired to deal with equations of physical motions.
- Ex. Geophysical Fluid Dynamics Laboratory (GFDL) Hurricane Prediction System (by Kurihara, Tuleya, and Bender, 1998)
- Statistical models
- Light-weight since only statistical formulas are used.
- Ex. Statistical non-parametric model (by Hall and Jewson, 2007)
- Statistical-dynamical models
- Allows large-scale variables as predictors.
- Ex. Statistical-dynamical model (by Wang et al., 2009)
- Ensemble or consensus models
- Gives a combination of predictions from different models, physical parameters, or initial conditions.
- Ex. Sparse Recurrent Neural Network (by Moradi Kordmahalleh, Gorji Sefidmazgi, and Homai-far, 2016)
However, since there are not enough collected hurricane observations, and the atmospheric systems are nonlinear and complex, the predictive ability of linear models is limited. Thus, a network that is capable of modeling the hurricane's time-dependent behaviours is desired.
Model Architecture
A recurrent neural network, which is capable of modeling nonlinear and complex sequential or dynamical relations between variables, would be used to model the hurricane's time-dependent behaviors. In this fully connected network RNN, the connection weights are the training parameters, which will be updated appropriately. The total time of the network is represented by [math]\displaystyle{ t=1,...,T }[/math] and the number of hidden layers is represented by [math]\displaystyle{ l=1,...,L }[/math] . Figure 1 below shows an example of RNN architecture with two hidden layers.
Forecasting Result
In this experiment, 32327 data provided by Unisys Weather data were used. The dataset is split into training sets and testing sets: 85% of the total hurricanes are used for training, and 15% are used for testing the accuracy of the model’s predictive performance. Each data involves five features: pressure, grid identification number, distance, direction, and wind speed. Figure 2 shows the predictive performance of the built grid-based RNN model on six randomly selected Atlantic Hurricane Trajectories. It can be seen that the grid-based RNN model predicts the hurricane trajectory location well since the real grid locations (black line in the figure) and the predicted grid locations (red line in the figure) match moderately well in all six randomly selected Atlantic Hurricane Trajectory.
Conclusion
The purpose of fitting this recurrent neural network over a grid system is to encapsulate the nonlinearity and complexity of hurricane trajectories prediction and improve accuracy of forecasting. For both training and testing data, our mean-squared error and root-mean-squared error were 0.01 and 0.11. Compared to “sparse RNN”, the biggest advantage of our RNN grid model is that we can train and predict any type of hurricanes, including loop hurricanes and monotonic hurricanes. Furthermore, by comparing to NHC methods which are currently used, our new method is also more accurate since a refined grid reduces truncation errors. Meanwhile, the RNN learns the behavior of a specific hurricane from a physical location to the next in time, instead of any hurricane in general as hurricanes trajectories can be quite different depending on different nonlinear and dynamic features. In addition, as the data size increases, the current model is so complex that making predictions becomes impractical, since each prediction takes too long to be made. In general, this paper is intended to introduce deep learning for making predictions of hurricane trajectories while being more lightweight and with improved accuracy in the model.
Critiques
Even though the final results of grid location predictions are quite accurate, there always exists an error between the predicted and real locations of the hurricanes, since the size of each grid block is not 1x1-degree scale to the real latitude and longitude. Then errors up to 50km could occur when translating the location information from grid location to be described in latitude and longitude. However, since the size of the grid depends on the amount of data points per unit area, a bigger dataset could reduce the error efficiently. In the future, artificial neural networks can be used to reduce the error caused by transformation. Also, combining the grid-based RNN method with Bayesian models will increase accuracy, because Bayesian models can quantify the uncertainty of prediction.