## 4 Numa Track and Evolution
The synoptic environment of Numa both at the surface and 500 hPa is shown by ECMWF operational analyses (Figure 2). On 16 November at 12:00 UTC (Figure 2a,b), a wide low pressure area (minimum 1004 hPa) is present over the Strait of Sicily and over the Ionian Sea, with two distinct minima. The mean sea level pressure (mslp) minimum over the Ionian Sea evolves in Numa, while the minimum over the Strait of Sicily is filled in the following hours. The wind at 900 hPa (red arrows) shows a cyclonic circulation over the Strait of Sicily and Ionian Sea, which is not completely closed around the Numa mslip minimum (Figure 2a). At 500 hPa, the synoptic situation shows a low of geopotential height over Southern Italy with two separate cut-offs. One of them is over the two mslp minima at the surface. Interestingly, the cyclone over the Ionian Sea, evolving in Numa, does not show a warm core surrounded by a close circulation at this stage of development (Figure 3a). Figure 1: (a) MODIS/Aqua on 17 November at 12:00 UTC; (b) MODIS/Terra on 18 November at 10:30 UTC. Figure 2: (a) Sea level pressure (hPa) and wind vectors (900 hPa) and (b) geopotential height (m) and wind vectors at 500 hPa on 16 November at 12:00 UTC. The well-defined mslp minimum, a warm core, as well as the closed cyclonic circulation at 850 hPa, start becoming evident between 16 November 18:00 UTC and 17 November 00:00 UTC (Figure 3b). The mslp on 18 November at 00:00 UTC is shown in Figure 4a. The cyclone center is located over the Sea, just offshore the southernmost tip of Apulia region. At 500 hPa (Figure 4b), the geopotential height shows a cut-off and a well-defined cyclonic circulation around its center, which is over the mslp minimum. At this stage of development, Numa clearly shows a warm core at several vertical levels (up to 300 hPa). In particular, at 700 hPa (not shown), the temperature gradient around the Numa center is \(\sim\)4 \({}^{\circ}\)C/120 km. During the following 12-18 h, the mslp and 500 hPa geopotential height minima were almost stationary in both position and value, causing rainfall and intense winds over Southern Apulia. Thereafter, the storm moved towards Greece while the mslp started to increase. Figure 5 shows the Numa track constructed from the mslp field provided by ECMWF operational analysis/forecast at 0.125\({}^{\circ}\). It illustrates the storm movement traced using the position of the mslp minima every three hours throughout 15 November to 19 November. During its evolution, Numa shows mslp minimum values ranging from 1006 hPa to 1003 hPa, higher than other Medicanes. Figure 5  
Figure 4: (a) Sea level pressure (hPa) and wind vectors (900 hPa) and (b) geopotential height (m) and wind vectors at 500 hPa on 18 November at 00:00 UTC. Figure 3: (a) Temperature and wind vectors at 850 hPa at 12:00 UTC on 16 November 2017. (b) As in (a) for 00:00 UTC on 17 November 2017. Only the zoom over the Ionian Sea is shown for clarity. shows also the lightning activity associated with the storm, as monitored by the LINET network. The total (both CG and IC) strokes detected within 200 km radial distance and within 1 h around the 3-hourly mslp minimum are shown. The persistence of the storm over Southern Apulia region is highlighted by the fact that the same position of mslp minima is found three times for two consecutive 3-hour time intervals between 17 November at 12:00 UTC and 18 November at 12:00 UTC. The temporal evolution of the storm in terms of lightning activity and mslp can be seen more in detail in Figure 6, showing the temporal evolution of mslp and the corresponding number of total strokes detected within 200 km radial distance and within 1 h around the location and time of the mslp minima. The figure evidences a more intense lightning activity at the initial stage of the storm when strokes are distributed around the cyclone center. This activity reaches its peak on 17 November at 12:00 UTC after the transition of the storm to the TLC phase.