Extended Forecast
Valid: Wed 15 Oct 2025 06:00 to Thu 16 Oct 2025 06:00 UTC
Issued: Mon 13 Oct 2025 21:48
Forecaster: TUSCHY

A level 2 was issued for E Sardegna and another one for Sicily and parts of S Italy mainly for excessive rain.

A level 1 surrounds both level 2 for similar hazards with lowered probabilities. A few waterspout events are possible next to isolated gusts with coastal convection.

SYNOPSIS

The yesterday mentioned structuring upper trough over the W Mediterranean Sea shifts leisurely SE during the forecast before broadening and turning quasi-stationary, as it awaits the next SE-ward racing Scandinavian trough, which could pick up at least parts of the trough's energy. The net result would be an induced eastward motion towards the Balkan States (beyond our forecast period).
In the meantime, we see a growing signal for a structuring depression SE of Sardegna, which is reflected both in ensemble data like IFS-ENS but also in numerous deterministic outputs. This vortex spin-up seems more like the collecting of various shallow positive PV anomalies over the W/CNTRL Mediterranean, which converge downstream of the upper trough and beneath the left exit region of a weak upper jet just S of Sardegna.

No change regarding the more hostile pattern for DMC activity over the rest of Europe with an ongoing highly amplified synoptic-scale wave pattern (blocking anticyclone over NW Europe and re-enforced troughing over Scandinavia into E Europe/W Russia).

Of concern is the advection of a moist/unstable airmass towards the Tyrrhenian Sea and therefore into the periphery of this evolving depression. A cocoon of humid/unstable air beneath the broadening and temporarily stationary upper trough creates a window of opportunity for a warm-core driven vortex to evolve with this mentioned depression due to the long lasting duration of diurnal driven clustering convection. It has to be seen where/when a more stable LL vortex evolves, which could then organize into a tropical-like cyclone. Latest guidance takes this vortex over the S-Tyrrhenian Sea in the Thursday/Friday time-frame, which is beyond our current guidance.

Independent of this potential development, the general setup has an high potential for regional excessive rainfall events with localized significant flash flooding over parts of S Italy.

DISCUSSION

... CNTRL Mediterranean ...

High uncertainties with this forecast persist and exist. The main question will be, which shallow positive PV anomaly becomes the main player during this forecast period. Either a growing MCV from the previous night could turn into a more dominant vortex or the mentioned signal of a LL vortex driven by the synoptic field could result in a structuring vortex. Dependant on its placement and strength, we deal with various scenarios of the expected wind field, which affects shear and placement of convergence zones but also the potential development of confined deformation bands along the periphery of any vortex.

When we combine ensemble and deterministic data, the current foci for training convection with excessive amounts arise

- over E Sardegna, in case we see a structuring vortex S and later SE of the Island, shifting E. Persistent easterly onshore flow with strengthening low-tropospheric flow and adequate CAPE create a confined swath for excessive rain. This risk lowers in case we see a more easterly placed vortex (SE Tyrrhenian Sea) growing out of an MCV event.

- along the coasts of Sicily and S Calabria, into the western Gulf of Taranto, where constantly strengthening southerly winds advect a moist/unstable airmass onshore. Coastal convergence serves as main reason for training convection but capping issues (especially over Sicily) could result in only a few/confined but intense clusters.

- offshore over the S Tyrrhenian Sea, where slow moving large thunderstorm clusters bring excessive rain, especially next to any more dominant vortex.

Any back-building cluster can produce hourly rainfall amounts in the 80-150 l/qm range with sub-6 hourly amounts in the 150-300 l/qm range. These amounts were observed during the past few days on a very local scale over the W Mediterranean with extreme gradients of rainfall amounts. Significant and life-threatening flash flooding is possible on a local scale with these amounts although it has to be emphasized, that only small parts of the level 2 area will see such extreme amounts. Right now the highest concern for such an event exists over extreme NE Sicily into S Calabria.

Coastal/offshore convection also poses a waterspout and gust risk.

The Gulf of Termini Imerese to the Gulf of Gioia were excluded from the level 2 as dried and better capped air keeps CI lower compared to the rest of the area. This dry bullseye is seen in ensemble and deterministic data.

Please be aware that these conditions spread gradually E beyond 06Z and affect the Ionian Sea thereafter. Please follow later updates (if any will be issued) and your local NMS for more information. Also keep in mind the potential development of a tropical-like vortex over the S Tyrrhenian Sea.