Page History

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1. Impact

Hurricane Florence made landfall in  North Carolina on 14 September as a category 1 hurricane. The cyclone brought torrential rainfall as it became quasi-stationary for a few days. At least 26 people was killed due to the cyclones.

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https://www.bbc.co.uk/news/world-us-canada-45563634

2. Description of the event

3. Predictability

3.1 Data assimilation

3.2 HRES

3.3 ENS

The plots below show the tracks (ensemble -grey, best track - black), position and intensity on 14 September 00UTC (ensemble - squares, best track - hourglass) in forecasts from 13 September (first plot) to 4 September (last plot). Early forecasts had problems to capture the northward "kink" on 7 September. The forecast from 4 September also had a majority of members turning northward over the Atlantic. This changed on the 5 September, and the sensitivity analysis further down is targeting this change. 

The plots below show the 4 most westerly (red) and easterly (green) in  the forecast from 4 September 12UTC (first plot), and the normalised difference in z500 between the cluster mean of westerly minus easterly members for 24h, 48h, 72h and 96h. The main sensitivity at 24 and 48 hours are in the easterly extent of the subtropical anticyclone. The anticyclone was weaker in the members going towards U.S.  

The plots below shows 3-day EFI and SOT for 3-day accumulated precipitation valid 14-16 September. In the earliest forecast presented here (from 8 September), the SOT is already high while EFI is low. This is a sign of a few extreme members in the ensemble. As the forecast lead time decreases, the EFI increases as well.

3.4 Monthly forecasts

The plots below show weekly strike probability (left) and normalised accumulated cyclone energy from extended-range forecasts, valid for 10-16 September. The earlier part of the hurricane season had been quite, and the extended-range forecast seems to picked up the signal of a more active period 2-3 weeks before.

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