Mesoscale Discussion
Valid: Wed 15 Oct 2025 08:00 to Wed 15 Oct 2025 13:00 UTC
Issued: Wed 15 Oct 2025 08:13
Forecaster: TUSCHY

This Mesoscale Discussion (MD) was issued to update the potential development of a warm-core driven vortex atop the S/SE Tyrrhenian Sea. Please keep in mind that the MD's validity does not match the time frame of thunderstorm activity, which extends well into the overnight hours.

Latest satellite data reveals an impressive cluster, which emerged over the CNTRL Tyrrhenian Sea during the past few hours. CTTs featured numerous intense/long-lived hot towers, which weakened during the past hours or so. However, this intense MCS with self-induced anticyclonic outflow into an upper jet over E Europe should induce enough latent heat release for an evolving positive PV anomaly at mid-levels. Latest gliders/floaters confirm SSTs in the 21-23C range, which is 1-1.5K above the SST climatology.

Finally, a passing weak upper jet to the S induces upper divergence atop the S Tyrrhenian Sea until the overnight hours and NWP guidance keeps a rather impressive upper divergence bullseye atop our area of interest.

Latest advected layered PW has plume of rich mid/upper level moisture advecting into the Tyrrhenian Sea area and latest NWP guidance indicates a cocoon of adequate BL moisture, although drier air could advect into any evolving vortex from the SE.

Right now there is no real support from any model to show a spin-up out of this MCS and latest scatterometer data also has no hints on anything (not yet capturing the ongoing MCS event). However we think that the current convection should spark at least a broader circulation and with the approaching diurnal convective minimum and constant eastward drift, there could be time issues before the vortex moves ashore over S Italy. On the other side, weakening convection could leave a slower moving vortex behind, which is ready for another round of diurnal driven convective activity with a downward building vortex later-on.

So despite not expecting any rapid spin-up, surrounding orography could help to increase probabilities for vortex stability/strength (e.g. by advection of coastal induced vorticity into any approaching vortex) beside the moderate thermodynamic and very favorable divergence background. At least a long-lived vortex should cross the SE Tyrrhenian Sea E and a slowly deepening warm-core vortex is forecast (into the overnight hours).

The main impact of any structuring vortex would be slow moving/training convection along its periphery (especially to the N and W of the vortex but also next the vortex' center). A few models show persistent nocturnal convection next to the vortex and induce gusts up to gale-force within a small area extending from S-Campania to W-Calabria (dependant on where any landfall will be).

Shear (especially in the lowest 3 km) increases S of the evolving vortex, so we could see enhanced probs. for organized DMC activity over Sicily and further E including a growing tornado risk with improving LL directional shear in a low LCL setup.

No major changes for the level 2 despite upgrading also the far SE part of the Tyrrhenian Sea mainly for an organized thunderstorm risk.