A huge waterspout reached the mainland of northern Italy on August 19 following heavy rain in the province of Genoa. In the coastal town of Arenzano, the waterspout caused damage to buildings and cars with a total coast of about 1 Meuro.

Some youtube videos:







and the impacts on the Arenzano beach



Some pictures:

www.ilsecoloxix.it/p/multimedia/liguria/...e.shtml?pag=1&code=2

and here

www.facebook.com/media/set/?set=a.552967...2952014828228&type=1

A personal weather station located in Arenzano recorded a wind burst of more than 100 km/h!

www.wunderground.com/personal-weather-st...819/e20140819/mdaily

This is a very interesting critical case, but probably too fine-scale to be modelled also with the DRIHM e-Infrastructure services, because we are speaking about phenomena active on the micro-β scale (20-200 m, Orlanski 1975).

Hi Antonio,

I actually remember seeing the last video being posted somewhere (website of a Finnish tabloid)!

There were also couple of pictures I found on flickr:

www.flickr.com/photos/roberto_1951/14997888161
www.flickr.com/photos/fotomie2009/14791270260
www.flickr.com/photos/38675231@N08/14969339171/

On 23 august 2014 around 1015am, the "twin waterspouts" made their appearance in front of Cogoleto beaches (2 km far apart Arenzano)



However this time they did not make "landfall", indeed a scenario not very common in the Mediterranean area

Indeed recently Keul et al (2009)

Keul, A. G., Sioutas, M. V., & Szilagyi, W. (2009). Prognosis of central-eastern Mediterranean waterspouts. Atmospheric Research, 93(1), 426-436.
www.sciencedirect.com/science/article/pii/S0169809508003128

formulated a waterspout forecasting methodology based on the estimation of

- Water – 850 mb temperature difference (ΔT)
- Convective cloud depth, EL – LCL (ΔZ)
- 850 mb wind speed (W850)

According to the Keul et al (2009) methodology:

- the synoptic type patterns associated with this waterspout episode was south-west flow (SW)



- cloud elevation EL can be estimated from the cloud top temperature and height (CTTH), developed within the SAF NWC context, aiming to support nowcasting applications. This product contributes to the analysis and early warning of thunderstorm development.



CTTH from EUMETRAIN on 19 august 2014, 06 UTC (Europe region). On the Gulf of Genoa area EL is about 8000-9000 m.

- The lifted condensation level (LCL) can be estimated from Lawrence (2005)

Lawrence, M. G. (2005). The relationship between relative humidity and the dewpoint temperature in moist air: A simple conversion and applications. Bulletin of the American Meteorological Society, 86(2), 225-233.

as LCL=25(100-RH), where RH is the relative umidity at 2 m, predicted by COSMO-2.8 and MOLOCH-1.5 (19 august 2014, 00UTC run): LCL=25(100-90)=250 m.

Thus AZ=EL– LCL=9000-250=8750 m

- The sea surface temperature, as provided by the buoy located at Capo Mele servizi-meteoliguria.arpal.gov.it/boacapomele.html, can be estimated around 24.5 C on 19 august

The 850 mb temperature can be estimated around 12.5 C, as predicted by COSMO-2.8 and MOLOCH-1.5 (19 august 2014, 00UTC run): then, ΔT=Water–850 mb temperature difference=24.5-12.5=12 C

- The condition on W850 ≤ 40 kts (about 20 m/s) is respected as well: the wind at 850 mbar was about 5 m/s

-All together the result provided by the Szilagyi Waterspout Index (SWI) is



The larger the value of SWI, the higher the probability of waterspouts developing: in this case the probability was predicted very MEDIUM being SWI around 5-6, and indeed the waterspout developed.

Interesting enough, with reference to the European Storm Forecast Experiment (ESTOFEX):

A level 2 was issued for eastern Greece, eastern Bulgaria and Black Sea mainly for excessive convective rainfall and isolated large hail.

A level 1 was issued for parts of North Sea, Denmark, Norway, Netherlands, Germany and Finland mainly for isolated excessive precipitation and tornadoes.

No reference to the Genoa Gulf area, thus confirming the quite controversial predictable nature of the Arenzano waterspout occurred on august 19, 2014.

Thank you Antonio!

In another paper on SWI I found the first graph (on first page) interesting in presenting different types of spouts in quite different conditions.

It also seems that relatively minor (local?) variation in the temperature difference in the area between 12 and 15 degrees would change the odds considerably. Do you think the "surprising" waterspouts are an indication of differences in actual temperatures or rather limitations of the model?

Apropos, it seems to have been a good waterspout summer in Finland, since I just remembered seeing this (happened already before the warning was issued):

www.iltalehti.fi/uutiset/2014081418574555_uu.shtml

Indeed the waterspout forecasting methodology here used is affected by many sources of uncertainties in the parameters estimation. Moreover it has not been developed specifically for the Mediterranean area.

That said we are testing it on the waterspouts observed in the last 10 years by the METAR data en.wikipedia.org/wiki/METAR provided by the Genoa airport

Stay tuned and new results will arrive soon

All the best

Antonio