[A-AS07] Analyses and Prediction of Extreme Weather and Climate in Southeast Asia

[AAS07-01] The rapid intensification of Typhoon Rai (Odette) and its impacts on the Philippines

★Invited Papers

*Gerry Bagtasa¹ (1.Institute of Environmental Science and Meteorology University of the Philippines)

Keywords:the Philippines, rapid intensification, typhoon, WRF model

Rapid intensification (RI) of tropical cyclones (TCs) is defined as the upper 95th percentile increase of TC maximum winds in a 24 hour period (25 kt). From 1951 to 2020, 28% of TCs that made landfall in the Philippines underwent RI. RI TCs pose a larger threat to the country as the region conducive for RI bounded by 123°-140°E and 10°-20°N is just to the east of the Philippines. Once a TC undergoes RI, it has a higher likelihood of having at least typhoon category on landfall, which results in greater impact. RI forecasts still have relatively low skill with threat scores ranging from 0.08-0.24. In the case of TY Rai, locally called Odette in the Philippines, a RI of 75 kt from 65 to 140 kt was observed from 0z 15 to 0z 16 of December 2021. The underestimated warning intensity may have caught many underprepared and resulted in widespread damages and loss of lives. The Weather Research and Forecasting model at 5 km horizontal resolution was utilized to diagnose the RI of TY Rai. The model was driven by the 1° NCEP-FNL and the 0.25° ECMWF ERA5 reanalysis data with sea surface temperature (SST) update and spectral nudging turned on. Using the 6-hourly skin temperature data of both initial and boundary conditions, model-estimated intensities were slightly lower than the JTWC warning intensity, nevertheless, the RI process that occurred on 15 December was captured by the model. Model results show a good relationship between the radial SST profile and the RI process where high SST near the TC eye region on 0z to 6z of 16 December resulted in convective bursts along the primary circulation of TY Rai, leading to its RI. The opposite case is true prior to its RI where the SST radial profile was near-constant which led to updrafts in the outer rainbands, thus inhibiting RI. In addition, the use of two observed SST data further emphasized the importance of SST radial profile where better stitching of satellite-derived SST yielded peak intensities closer to the recorded intensity warnings.