Predicting tropical cyclone rapid intensification using the 37 GHz ring pattern identified from passive microwave measurements

A distinctive satellite‐derived precipitative ring pattern around the tropical cyclone (TC) center is found to be related to rapid intensification (RI). The ring pattern appears on the Naval Research Laboratory (NRL) 37 GHz passive microwave composite color product as a cyan color ring. The probability of RI is evaluated for cases with this ring pattern by reviewing images of the NRL product for 84 TCs during 2003–2007 in the Atlantic basin using 6‐hourly National Hurricane Center (NHC) best track data. It is found that when combining the ring criterion with the Statistical Hurricane Prediction Scheme (SHIPS) RI Index (RII), the probability of RI almost doubled, indicating that both the ring and SHIPS RII contain independent information for RI prediction. A subjective technique for predicting RI is proposed using both the 37 GHz ring and the SHIPS RII. Both the probability of detection (POD) and the false alarm ratio (FAR) for the combined ring+SHIPS RII are lower than those for SHIPS RII alone (POD, 24% versus 77%, and FAR, 26% versus 66%) when treating every 6‐hr synoptic time as a separate case. Since the method was initially developed for RI event‐based forecasts, statistics based on 2003–2007 Atlantic RI events, which consist of a contiguous period where any 24‐hour subset shows at least a 30 kt intensity increase, are also generated. The method captures 21 out of these 28 events and produces 2 false alarms, producing a POD of 75% and a FAR of 9%.