Storm Forecast
Valid: Fri 17 Nov 2017 06:00 to Sat 18 Nov 2017 06:00 UTC
Issued: Thu 16 Nov 2017 23:04
Forecaster: DAFIS
A level 1 was issued for SE Italy, Greece and W Turkey mainly for large hail, severe wind gusts and excessive precipitation. Waterspouts are expected in Ionian and Aegean Seas.
SYNOPSIS and DISCUSSION
The cut-off low in Central Mediterranean is gradually weakening and mid-levels are warming due to the ongoing marine DMC. At the surface below, a warm-core vortex has formed just SE from Italy, verified by Suomi NPP/ATMS (ch8) brightness temperature, with high low-level PV values. Models predict that SBCAPE will remain in the range of 600-1200 J/kg over Ionian Sea, and thunderstorms will continue to develop near the center of the system. Even though global NWP models show the SLP dropping near 1010 hPa, LAMs forecast a more vigorous system with a core pressure even below 990 hPa, but it will be extremely difficult to verify the actual values since the vortex will remain away from the coast and surface observations are limited to cargo ships. The latest GFS run shows the system approaching SE Italy in the morning of Friday, where severe convective and non-convective wind gusts will be the main threat (25 30 m/s). Moreover, thunderstorms will be able to produce flash floods near the coast, due to the slow motion and saturated vertical profiles.
Since the strength of this vortex is directly linked to the latent heat release processes associated with DMC and sea-surface fluxes, LAMs suggest very different solutions, even those using the same initial and boundary conditions. So, the final track of the vortex remains unknown, probably approaching Greece in the morning of Saturday, after the end period of this outlook. Nevertheless, wind speeds at the range of 30 50 m/s pose a serious threat for ships and marine infrastructures.
More to the east of the aforementioned cyclone, very humid masses exist over Greece, overlapping with steep lapse rates over the Aegean Sea where local large hail events may verify. SBCAPE in the range of 1000-1600 J/kg and 15-20 m/s DLS create a favorable environment for hail up to 3 cm in diameter. In north parts of Greece, a strong convergence zone is placed for the third consecutive day (already 250-300 mm of rainfall), where we forecast flash floods due to training convection, but with limited lightning activity. During the night of Friday and morning of Saturday, only marine thunderstorms should be found over our domain, in NE Aegean and Ionian Seas.
Finally, waterspouts can form in Ionian and Aegean Seas. In SE Italy, strong vorticity near the coasts as the cyclone approaches, increase the probability of tornadoes. In Aegean Sea, weakening low-level wind field and strong instability also increases the chances for waterspout develoment.
