Medicane Numa over the Ionian Sea

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Numa was a Mediterranean tropical-like cyclone, or Medicane, with the properties of a subtropical cyclone.

Medicane Numa
Date & Time
15 November 2017 12:00 UTC–19 November 09:00 UTC
Meteosat-9 & 10, Suomi-NPP
Airmass, True Color RGB, Natural Color RGB, Infrared, High Resolution Visible, Cloud Type RGB, Cloud Phase RGB

By HansPeter Roesli (Switzerland) and Djordje Gencic (RHMSS)

On 13 November a deep Genoa low started to pushed polar air in the direction of southern Italy. From 15 November onwards the depression widened and moved to the Central Mediterranean. In particular, over the still warm Ionian Sea (between southern Italy and Greece) the cold and now very humid airmass destabilised under weak vertical wind shear.

These were the necessary ingredients for the formation of a Medicane, a MEDIterranean hurriCANE, or Tropical-Like Cyclone (TLC).

Taking on the name Numa, on 18 November it appeared as a whirl of convective cloud and a distinct quasi cloud-free eye. The structure was short-lived — by the evening of 18 November the Medicane had dissipated due to a trough and increased wind shear.

The evolution of Numa can be followed in the sequence of Meteosat-10 Airmass RGBs from 15–19 November (MP4, 28 MB). The TLC-phase on 18 November is shown in a sequence of HRV images overlaid in semi-transparency by the false-coloured IR10.8 band, both from the rapid-scanning Meteosat-9 between 06:00 UTC and 15:00 UTC (MP4, 10 MB).

Figure 1 (above right, click to expand) is four images from SNPP VIIRS on 18 Nov at 12:14 UTC (like Figure 2) which show in clockwise order the Natural Colour RGB (NCOL), the false-colour temperature map from band IR10.763 (M15), the Cloud Type RGB (CTYP) and the Cloud Phase RGB (CPHA). Note that in particular in the NCOL frame there isolated strangely-coloured pixels due to specular reflection of the sunlight.

Figure 2: SNPP, 18 Nov, 12:14 UTC
VIIRS True Color RGB
Figure 3: Met-9, 18 Nov, 12:00 UTC
High Resolution Visible with MSLP charts and GFS analysis overlaid

A True Color RGB of the VIIRS imager on Suomi-NPP shows some more details of the cloud structures shortly after 12:14 UTC (Figure 2).

Another typical feature of a hurricane is its warm core. As shown by the composite of the HRV band with the charts of MSLP and equipotential temperatures from the Global Forecast System (GFS) analysis (Figure 3) Numa at 12:00 UTC on 18 November had its eye collocated with the MSLP centre and a warm 700 hPa area.



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