# Typhoon Intensity Forecasting Based on LSTM Using the Rolling Forecast Method
## 2 Study Area and Data  
In the experiment, typhoons that occurred in the Northwest Pacific were studied. Typhoons that occurred in other areas were outside the scope of this study. The data for the experiment were from the best tropical cyclone track data set every 6 h [22] from the Tropical Cyclone Data Center of the CMA (tcdata.typhoon.org.cn, accessed on 14 January 2021). These typhoon data include the intensity and position information of typhoons occurring in the Northwest Pacific every 6 h from 1949. Data of the samples of each typhoon case can be seen in Table 1. In Table 1, the latitude (a positive value indicates north latitude) and longitude (a value smaller than 1800 indicates east longitude, a value bigger than 1800 west longitude) are 10 times that of the real values. For example, if the latitude is 95, the real value is 9.5. Because the number of typhoons in 2015 (Figure 1) was higher than in other years, as well as the number of typhoons that reached the strong typhoon and super typhoon levels, the data from 2000 to 2014 were used to train and test the prediction models; for the former, seventy percent of the data were used to train the models, while the remainder were used to test them, and typhoons Chan-hom and Soudelor (2015) were used to validate the models. Additionally, the typhoon cases that did not reach the typhoon level were not used in the experiment so as to avoid the negative effects for typhoon intensity forecasting and to achieve better prediction results. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Date (YYYYMMDDHH)** & **Intensity Level** & **Latitude** & **Longitude** & **Minimum Pressure (h Pa)** & **Maximum Wind Speed (m/s)** \\ \hline
2015063000 & 1 & 95 & 1607 & 1000 & 15 \\
2015063006 & 1 & 98 & 1601 & 1000 & 15 \\
2015063012 & 2 & 100 & 1595 & 998 & 18 \\
2015063018 & 2 & 101 & 1587 & 995 & 20 \\
2015070100 & 2 & 105 & 1575 & 995 & 20 \\
2015070106 & 2 & 110 & 1566 & 995 & 20 \\
2015070112 & 2 & 113 & 1556 & 992 & 23 \\
2015070118 & 3 & 113 & 1543 & 990 & 25 \\
2015070200 & 3 & 111 & 1528 & 990 & 25 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The data of each typhoon case. The maximum wind speed (WS) and the minimum pressure (P) near the typhoon's center, as well as the latitude (Lat) and the longitude (Lon) of the typhoon's center were included in the data source. Additionally, the moving speed (MS) of the typhoon was also considered in the experiment. According to the theory of the cosine function and triangle function, the moving speed of a typhoon can be calculated as follows:  
\[c=\frac{111*Lat_{2}*\left|Lon_{2}-Lon_{1}\right|}{90} \tag{1}\]  
\[MS=\frac{1}{t}*\sqrt{(Lat_{2}-Lat_{1})^{2}+\frac{Lat_{2}*c^{2}}{Lat_{1}}} \tag{2}\]  
where \(Lat_{1}\) and \(Lon_{1}\) are the latitude and longitude in the previous 6 h, respectively; \(Lat_{2}\) and \(Lon_{2}\) are the latitude and longitude at the current time, respectively; \(t\) is the interval time between two adjacent samples (the value of \(t\) was six in the experiments). In addition, an MS of zero indicates a typhoon case that is motionless during the previous 6 h. The descriptive statistics of these variables of the processed typhoon data are shown in Table 2.  
The variables and prediction factors in this experiment can be seen in Table 3. In Table 3, P(t), P(t-1), P(t-2), P(t-3), and P(t-4) refer to the data of minimum pressure at the current time, in the previous 6 h, in the previous 12 h, and in the previous 18 and 24 h, respectively, which can be seen as the prediction factors based on the minimum pressure. Similarly, the following four rows of Table 3 display the data of the maximum wind speed, the latitude, the longitude, and the moving speed, respectively, which can be seen as the prediction factors based on the variables WS, Lat, Lon, and MS, respectively.