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In the middle of December the post-landfall cyclone related to TC Jasper caused severe rainfall over Queensland, Australia. Following on from the passage westwards the tropical cyclone, across northeast Australia, legacy moisture and slow-moving low level circulations have had a profound impact on local communities, as up to 2m of rain fell in a few days (see here for news/discussion: https://www.theguardian.com/australia-news/2023/dec/19/cyclone-jasper-how-did-it-cause-so-much-rain-and-could-global-heating-be-to-blame). Data from the wettest site, with a complete record, that I could find on the BOM website - namely "Whyanbeel Valley" - is shown below. It lies about 70km NW of Cairns, which was also badly affected. Here you can see 699mm for the most recent 24h period.
https://en.wikipedia.org/wiki/Cyclone_Jasper
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2. Description of the event
In this evaluation we will focus on the rainfall over three periods: 5-day rainfall 13-18 December plus 1-day rainfall on 13 and 17 December. The focus region is the coastline of Queensland (land points inside 15.5S - 17.5S, 145E- 146E).
The plots below show analyses of MSLP and 6 hour rainfall from 11 December 00UTC to 18 December 00UTC, every 12th hour. TC Jasper made landfall on 13 December, but later stalled over Queensland, while the rainfall continued. On 17 December the rainfall intensified.
Observed rainfall from Whyanbeel valley:
3. Predictability
3.1 Data assimilation
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The plots below shows EFI and SOT for 1-day precipitation (13 December 00UTC - 14 December 00UTC) from different initial dates.
The plot below shows the forecast evolution plot for 1-day precipitation (13 December 00UTC) in land-points inside the box outlined in the plots above. Concatenated 6-hour forecasts - green dot, ENS control –red, ENS blue box-and-whisker, Model climate – cyan box-and-whisker. Ensemble mean as black diamonds. Triangle marks the maximum in the model climate based on 1800 forecasts.
The problem for the forecast on 13 December is obvious here, and is probably related to the data assimilation issue discussed in Section 3.1.
The plots below shows EFI and SOT for 1-day precipitation (17 December 00UTC - 18 December 00UTC) from different initial dates.
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