Since yesterday, a well structured cold-core low looped cyclonically atop Corsica and is currently situated roughly at 40°30' N and 8-9° E, featuring an E-W elongated center. Also, mid-tropospheric vortex built downwards and 19Z ASCAT scan featured a 15-20 kt surface depression just to the NW of Sardinia which moved east/southeastwards since then. A 30-35 kt surface wind maximum along its northern/western fringe is not correlated with the organizing surface circulation but exists rather due to a channeled gradient flow. Just before landfall over N-Sardinia, DMC increased in strength and organization next to the center but decreased markedly after landfall. An increase in DMC was noted along the northern/northeastern fringe due to increasing LL convergence.
During the start of the forecast period, the depression's center should emerge off of Sardinia into the N-Tyrrhenian Sea and therefore further to the north than most models indicated 24 h ago. However, due to the asymmetric and elongated circulation center and movement atop the rough orography of Sardinia, uncertainties still exist if the center may reform a bit more to the south. Anyhow, this motion brings the depression's center atop an anticyclonic eddy with SSTs of 27-28 °C / positive SST anomalies of 2-3 K and good heat content. As the cyclonic vortex is not yet vertically stacked, some slow eastward motion is still expected with a more or less quasi-stationary motion over the far NE Tyrrhenian Sea during the end of the forecast. At that time, SSTs decrease by roughly 3K. Despite a gradual warming trend of the mid-/upper level vortex and an increase of the geopotential heights as a response of the more zonal flow pattern over N-Europe, background environment remains supportive of a temporarily confined core modification. DLS is already weak and continues to weaken with some weak upper divergence forecast.
A lot depends on the final track of the depression, but confidence increases that a subtropical cyclone may evolve between Sardinia and C-Italy during the forecast. Still a few high resolution models indicate moderate to rapid intensification and is was noted that overall model tendency approached the shallow warm core phase in FSU phase diagrams. Surrounding sounding data also confirm a decrease of the dry slot strength and ongoing moistening, so overall environmental conditions seem supportive for strengthening/organization. An intensity forecast is hard to create due to
a) proximity to the islands/Italy
b) potential infiltration of more stable stratified, rain cooled air from N-C Italy during the forecast
c) uncertainty how strong/persisting convergence and DMC east of Corsica may affect the development of the depression's center and attendant banding structure
Especially in case of the depression's motion atop the warm eddy, we would not rule out a ST 2.5 classification, which would equal 35-40 kt . In any case, the feature will be closely monitored during the following 24 hours.