The quagmire of arrested development in tropical cyclones Weather and Forecasting

Forty-eight hour intensity forecasts for Hurricane Pamela (2021) from numerical weather prediction models, statistical–dynamical aids, and forecasters were a major forecast bust with Pamela making landfall as a minor rather than major hurricane. From the satellite presentation, Pamela exhibited a symmetric pattern referred to as central cold cover (CCC) in the subjective Dvorak intensity technique. Per the technique, the CCC pattern is accompanied by arrested development in intensity despite the seemingly favorable convective signature. To understand forecast uncertainty during occurrences, central cold cover frequency from 2011–2021 is documented. From these cases, composites of longwave infrared brightness temperatures from geostationary satellites for CCC cases are presented and the surrounding tropical cyclone large-scale environment is quantified and compared with other tropical cyclones at similar latitudes and intensities. These composites show that central cold cover has a consistent presentation, but varies in the preceding hours for storms that eventually intensify or weaken. And, the synoptic-scale environment surrounding the tropical cyclone thermodynamically supports the vigorous deep convection associated with CCC. Finally, intensity forecast errors from numerical weather prediction models and statistical–dynamical aids are examined in comparison to similar tropical cyclones. This work shows that guidance struggles during CCC cases with intensity errors from these models being in the lowest percentiles of performance, particularly for 24- and 36-h forecasts.

针对2021年飓风帕姆（Hurricane Pamela）的48小时强度预报，源自数值天气预报模式（numerical weather prediction models）、统计-动力辅助预报工具（statistical–dynamical aids）以及专业预报员的研判均出现重大失误——帕姆最终以弱飓风而非强飓风等级登陆。卫星图像显示，帕姆呈现出对称云型，在主观德沃夏克强度定强技术（subjective Dvorak intensity technique）中，该云型被称为中心冷云盖（central cold cover, CCC）。根据该定强技术，尽管存在看似有利的对流特征，中心冷云盖云型往往伴随强度发展停滞。为厘清该现象出现时的预报不确定性，本研究统计了2011至2021年间中心冷云盖的出现频次。基于上述案例，本研究绘制了中心冷云盖案例的静止卫星长波红外亮温合成图，并量化分析了对应热带气旋周边的大尺度环境场，同时将其与同纬度、同强度的其他热带气旋进行对比。这些合成分析结果表明，中心冷云盖云型具有一致的形态特征，但对于最终增强或减弱的风暴而言，其出现前的小时数存在差异。此外，热带气旋周边的天气尺度环境场在热力学层面支持与中心冷云盖相关的强深厚对流活动。最后，本研究将数值天气预报模式与统计-动力辅助预报工具的强度预报误差，与同类热带气旋的预报误差进行对比分析。本研究表明，此类预报指导工具在中心冷云盖案例中表现不佳，相关模式的强度预报误差处于性能表现最差的百分位区间内，尤其在24小时与36小时预报时段表现最为显著。