Challenges in the Forecasting of Severe Typhoon Koinu in 2023
<p>Provisional best track of Severe Typhoon Koinu and (insert) its track near Hong Kong (Hong Kong Time (HKT) = UTC + 8 h). The movement of Koinu was slow and erratic during 6–8 October 2023.</p> "> Figure 2
<p>(<b>a</b>) Surface weather chart at 1200 UTC on 8 October 2023 as analyzed by the Hong Kong Observatory (HKO), where Koinu was at its closest to Hong Kong. Koinu had a small circulation, and the northeast monsoon dominated over Southern China. (<b>b</b>) Infrared satellite image of Himawari-9 Satellite of the Japan Meteorological Agency at 1200 UTC on 8 October 2023 showing Koinu just to the south of Hong Kong. (<b>c</b>) HKO radar image at 1200 UTC on 8 October 2023. Koinu had a compact eye, estimated to be less than about 30 km in diameter.</p> "> Figure 3
<p>Models’ forecast tracks of Koinu at 1200 UTC run on 2 October 2023. Also shown on each panel is Koinu’s analysis positions (black) based on HKO operational analysis track. (<b>a</b>) Forecast tracks from ECMWF, JMA, NCEP, UKMO, and TRAMS. (<b>b</b>) Forecast tracks from AI models Pangu-Weather and Fengwu; both were initialized by the operational analysis of ECMWF.</p> "> Figure 4
<p>Models’ forecast tracks of Koinu at 1200 UTC run on 6 October 2023. Also shown on each panel is Koinu’s analysis positions (black) based on HKO operational analysis track. (<b>a</b>) Forecast tracks from ECMWF, JMA, NCEP, UKMO, and TRAMS. (<b>b</b>) Forecast tracks from AI models Pangu-Weather and Fengwu; both were initialized by the operational analysis of ECMWF.</p> "> Figure 5
<p>ECMWF’s operational analysis of (<b>a</b>) 700 hPa relative humidity (color-filled contours) and winds (barbs and streamlines), as well as (<b>d</b>) mean seal-level pressure (contours) at 1200 UTC on 8 October 2023. Note that according to the HKO operational analysis, Koinu was at that time still a typhoon with central pressure 975 hPa and maximum sustained winds 75 kt. (<b>b</b>,<b>e</b>) 96 h forecast of ECMWF valid for 12 UTC, 8 October 2023, where Koinu was forecast to be dissipating possibly due to significant dry intrusion from the northeast monsoon, while its remaining surface vortex would have been pushed southwestwards by the monsoon. (<b>c</b>,<b>f</b>) 96 h forecast of TRAMS valid for the same time. TRAMS successfully forecast Koinu to remain as an intense and intact tropical cyclone at its closest to Hong Kong.</p> "> Figure 6
<p>500 hPa geopotential height with a contour interval of 1 dam. The 5880 m contours are plotted in red. ECMWF’s operational analysis at 1200 UTC on (<b>a</b>) 7 and (<b>b</b>) 8 October 2023. Note the evolution of 5910 m geopotential height contour for the establishment of a ridge over northern part of South China Sea. (<b>c</b>–<b>e</b>) 48 h forecast from ECMWF, NCEP, and UKMO respectively, valid for 1200 UTC on 8 October 2023. None of these models were able to fully capture the extent and strength of the ridge to the southeast of Koinu. (<b>f</b>) 48 h forecast of Fengwu initialized by the operational analysis of ECMWF, valid for 1200 UTC on 8 October 2023, where the ridge to the southeast of Koinu was most accurately forecast among available models.</p> "> Figure 7
<p>EPS strike probability maps of Koinu based on the ensembles of ECMWF, NCEP, and UKMO from 1200 UTC runs on (<b>a</b>) 30 September and (<b>b</b>) 2, (<b>c</b>) 4, and (<b>d</b>) 6 October 2023. Also shown is Koinu’s analysis positions (black) based on HKO operational analysis track.</p> "> Figure 8
<p>Root-mean-square error of models’ forecast positions for Koinu as a function of lead time. Forecasts are verified against Koinu’s analysis positions based on HKO operational analysis track and have a common dataset among different models.</p> "> Figure 9
<p>Intensity of Koinu as forecast by models from 1200 UTC runs on (<b>a</b>) 30 September and (<b>b</b>) 2, (<b>c</b>) 4, and (<b>d</b>) 6 October 2023. The light-red shading indicates the spread of all available models. Also shown is Koinu’s analysis intensity (black line) based on HKO operational analysis track. The red rectangle indicates the time period where Koinu at its closest approach to Hong Kong.</p> "> Figure 10
<p>Root-mean-square error of models’ forecast sustained maximum winds for Koinu as a function of lead time. Forecasts are verified against Koinu’s analysis intensity (in knots) based on HKO operational analysis track and have a common dataset among models.</p> "> Figure 11
<p>Forecast 10 m surface wind fields over the Pearl River Estuary in 6-hourly intervals valid from 0000 UTC (leftmost column) to 1800 UTC (rightmost column) on 8 October 2023, by models initialized at 1200 UTC on 7 October 2023. Forecast winds are colored in accordance with the Beaufort scale, specifically, hurricane-force winds in yellow, which might come to the doorstep of Hong Kong. (Top row) ECMWF. (Second row) NCEP. (Third row) JMA. (Fourth row) TRAMS.</p> "> Figure 12
<p>Models’ 24 h accumulated rainfall forecast for 9 October 2023, with three consecutive runs showed on the top (initialization time 20231008 00Z), middle (initialization time 20231007 12Z), and bottom rows (initialization time 20231007 00Z). The four columns starting from the left are, respectively, ECMWF, NCEP, JMA, and TRAMS model output. TRAMS was able to predict the most accurate magnitude of local rainfall on 9 October 2023 following the passage of Koinu, but its most recent run (on top row) oppositely turned down the rainfall forecast; such a wrong trend was also given by other global models.</p> ">
Abstract
:1. Introduction
2. Major Challenges of the Forecast of Koinu
3. Track Forecast
4. Intensity Forecast
5. Wind Forecast
6. Rainfall Forecast
7. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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He, Y.-H.; Chan, P.-W. Challenges in the Forecasting of Severe Typhoon Koinu in 2023. Atmosphere 2024, 15, 31. https://doi.org/10.3390/atmos15010031
He Y-H, Chan P-W. Challenges in the Forecasting of Severe Typhoon Koinu in 2023. Atmosphere. 2024; 15(1):31. https://doi.org/10.3390/atmos15010031
Chicago/Turabian StyleHe, Yu-Heng, and Pak-Wai Chan. 2024. "Challenges in the Forecasting of Severe Typhoon Koinu in 2023" Atmosphere 15, no. 1: 31. https://doi.org/10.3390/atmos15010031