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The figure above shows forecasts initialised 25 Oct 0 UTC (+84h).
4.1.3 Mesoscale Structure
Mean wind speeds and wind gusts are not just dependant on low depth. The multiple possible scenarios provided by HRES and ENS, in O- and E-suites, have shown considerable sensitivity, in different parts of the storm - that make the difference between a normal windstorm, and a once-in-a-lifetime event. Pinning this down is the real challenge. The following plots illustrate some of the issues - they have been extracted from animations in Ervin's daily reports, linked to above.
The top row in each table cell is from the O-suite; the bottom row from the E-suite.
The left table column shows gusts, the right mean 10m winds.
Validity times are 03 (top row of table), 04 (middle) and 05UTC (bottom), with gusts being the maximum in the hour up to that time.
| Max 10m gusts (in preceding hour) | 10m mean speed | |
| 03UTC |  |  |
|---|---|---|
| 04UTC |  |  |
| 05UTC |  |  |
| Gust scale: 20-green-24-26-28-30-orange-32-red-34-magenta-37-40 (m/s) |
First thing to note is the huge variability in the warm sector due E of the low centre, variability which does not appear to relate to geostrophic or gradient winds, both of which look, to the eye, to be relatively unvarying, and also much the same in 0- and E-suites in this region.
Next note how the gusts jump around between successive times - eg in the E-suite we go from locally 30m/s over Kent on the first frame, to widely only 25m/s two hours later. Gusts over the sea also appear to be reducing markedly in that time frame, despite no clear reduction in gradients.
4.2 ENS
The sequence of figures above shows the strike probability of cyclone with maximum wind speed (mean) over 60 kt (31 m/s) at 1 km height. The plots are valid for the 28 October (24-hours). The first forecast is from 28 Oct 0 UTC and one day is added for each plot. With longer lead time the feature is delayed (too slow) in the model, but the path of the cyclone seems very consistent up to 6 days before the landfall.
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