A Rapid Intensification Warning Index for Tropical Cyclones Based on the Analog Method.

Prediction of the rapid intensification (RI) of tropical cyclones (TCs) remains challenging. In this paper, by using information from the early period following TC formation, the rapid intensification warning index (RIWI) is developed based on the analog method. A 10‐year cross‐validation and data from Hurricane Ida (2021) are used to verify its potential application. Results show that the RIWI can efficiently discriminate between RI and non‐RI storms and has a significant positive correlation with the lifetime maximum intensity (LMI) of the TCs. By using this index, an early warning can be issued ∼30 hr before the onset of RI, which is much earlier than the predictions made using the probabilistic Statistical Hurricane Intensity Prediction System RI index. In addition, by using the RIWI as a predictor, the prediction of LMI provides an early estimate of TC severity. Plain Language Summary: Variations in the intensity of tropical cyclones (TCs) are difficult to forecast, especially the occasional TCs that develop quickly over a period of couple of days; that is, rapid intensification (RI). Recent studies have demonstrated that it is easier to forecast RI likelihood than RI timing. Thus, instead of attempting to forecast the exact timing of RI, it may be more useful to predict whether RI will occur during the lifetime of a TC. In this paper, by using information from the early stage of TCs, we use the analog method to develop the RI warning index (RIWI). Then, using an appropriate threshold, it can be used to predict whether RI will occur during the lifetime of a TC. Furthermore, an important TC parameter, the lifetime maximum intensity (LMI) of the TC, has a significant positive correlation with its RIWI. The application of RIWI to Hurricane Ida (2021) is also presented in this paper and shows that an early warning can be issued ∼30 hr before the onset of RI. Key Points: By using the information of tropical cyclones (TCs) early stage, a rapid intensification warning index (RIWI) is constructed based on the analog methodThe RIWI can distinguish between rapid intensification (RI) and non‐RI storms during the early stages of TCsThere is a significant positive correlation between a TC's RIWI and its lifetime maximum intensity [ABSTRACT FROM AUTHOR]