202008 - Tropical Cyclone - Laura

Status: Finalised Material from: Linus

1. Impact

On 27 August the tropical cyclone Laura made landfall on the U.S south-coast in the western Louisiana as a category 4 hurricane, making it the 10th most intense cyclone to make U.S landfall based on maximum wind speed (according to Wikipedia). Around 30 people were killed in Hispaniola and in the U.S respectively.

2. Description of the event

The tropical cyclone originated from a tropical wave coming out from the western Africa around the 15 August. The cyclone was recognized as a tropical storm on 21 August while being east of the Leeward islands. The cyclone passed over land on Hispaniola and Cuba, and entered the Gulf of Mexico on 25 August as a weak cyclone.

The plots below show analyses of MSLP and 6-hour forecasts of precipitation from 26 Aug 00UTC to 27 Aug 12UTC, every 12th hour.

3. Predictability

3.1 Data assimilation

3.2 HRES

3.3 ENS

The plots below show EFI for 24-hour maximum wind gusts valid 27 August. The hourglass symbols marks Galveston, Texas.

The plot below shows the forecast evolution plot for 24-hour maximum wind gusts in Galveston, Texas on 27 August. The plot includes ENS (blue box-and-whisker), HRES (red dot) and the model climate (red box-and-whisker). The forecasts around 25 August indicated landfall close to Galveston, before the forecast moved the predicted cyclone further to the east and spared the Houston metropolitan the extreme conditions.

The plots below show the tropical cyclone track for the operational ECMWF forecasts. The symbols shows the position on 27 Aug 00UTC. HRES (red), ENS CF (blue), ENS PF (grey) and BestTrack (black).

3.4 Monthly forecasts

The plots below show the weekly strike probability for forecasts valid 24-31 August. Note the decrease in strike probably in the forecast from 20 September (second plot) compared to 17 August (third plot).

3.5 Comparison with other centres

The plots below show track from ECMWF (left), GEFS (middle) and MOGREPS (right). The symbols show the position on 27 Aug 06UTC. The plot for ECMWF include HRES (red) and ENS CF (blue). BestTrack in included in black with circles every 6 hour and the position on 27 Aug 06UTC as hourglass. All forecasts had problems to capture (1) the northward shift in the observed track between 25 Aug 12UTC and 26 Aug 00UTC, and (2) the curve to the north on before the landfall. Some of the model runs had a northward bias in the early part that compensated (1).

26 Aug 00UTC