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In general, analysis of IFS model performance suggests:

• HRES CONTROL-10 errors in forecast positions of tropical cyclones are on average less than 200 km at Day3 and less than 350 km at Day5.
• Broadly, the IFS models tend on average to move tropical cyclones rather too slowly (by about 1-2 km h^-1).
• Strike probabilities seem to be a little high.  This applies to TCs in existence at T+0, but in in view of some conflicting results this topic is currently undergoing further investigation (Nov 18).  ECMWF plans to start verifying the 'activity' product soon.
• The IFS models handle rapid intensification of tropical cyclones rather poorly.  It is quite common to see an under-estimate of the speed of intensification during periods of intensification.
• HRES CONTROL-10 errors in central pressure are erratic.  They have a relatively small average bias though tend to over-deepen the central pressure.  The ENS Control run is generally not deep enough by around 15 hPa.   
• There is on average an under-estimation of maximum winds in the circulation, particular during periods of rapid intensification.
• Results are mixed regarding genesis of tropical cyclones:

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Fig8.1.10.3.2: IFS model forecast location error of tropical cyclones (HRES CONTROL-10 - blue; Ensemble Mean (EM) - Yellow)  and ENS spread (Red dots).  The diagram indicates that in 2016 the average location error and spread at:

• Day3: HRES CONTROL-10 location error about 180km; EM location error about 190km; ENS spread about 190km.
• Day5: HRES CONTROL-10 location error about 340km; EM location error about 320km; ENS spread about 310km.

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Fig8.1.10.3.3: An illustration of what can happen when the model resolution is increased.  HRES CONTROL-10 model performance Aug-Nov 2015 using test runs (~9km resolution - Red;  ~16km resolution - Blue), both without ocean coupling. On average, ~9km resolution forecast location error is slightly better to about Day5 but marginally worse from Day5 to Day7.  However, beyond about Day5 the low sample size makes statistics unreliable and ~9km resolution is unlikely to be significantly different to ~16km resolution. Users should note that this diagram is included to illustrate that  resolution changes have a significant impact. With the introduction of

Before ocean-atmosphere coupling in HRES in cycle 45r1, was introduced in June 2018 , characteristics of the behaviour of HRES have changed somewhat. For example there was a tendency to over-deepen , which is very apparent here, has been reduced. New plots will be added to the User Guide once we have a large enough sample.cyclones.

Analysis Aspects

Interpretation of Increments near Tropical Cyclones

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• the threat area in eastern USA is broadened.
• there is less chance that the hurricane track will curve northwards off the eastern seaboard.
• the southern flank of the threat extends southward into Florida.
• HRES CONTROL-10 (and ENS mean) make more progress westwards into USA.

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General Forecast Information

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CONTROL-10 versus ENS

One of the consequences of the high spatial resolution of HRES is HRE is that, compared to the ENS, it responds more readily to the changes in the evolving structure of the modelled atmosphere.  This can be especially evident when there is extensive active convection, and the mean sea level pressure in the vicinity can often be forecast to fall, sometimes steeply, with a consequent increase in the low altitude wind circulation (for developing tropical storms). The track of these low pressure centres can vary significantly from run to run according to variations in the low pressure structure. Users should always compare HRES forecasts with corresponding ENS member forecasts.  Nevertheless, HRES should generally be considered as a more probable member of the ensemble, particularly with regard to central pressure, and should not be discarded just because of major differences in intensification rates or in the subsequent low track.  Indeed HRES can often give early indication of the development of small or vigorous circulations and the associated strong and potentially dangerous winds.

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