Topic: Waterspout forcasting

[nmoir]

Interesting and useful piece on how to forcast for waterspouts.

[Michael Thomas]

Thanks for the article.

One thing that stuck me though was this - in the nomogram of convective cloud depth vs difference in sea and 850 mbar depths they find that the majority of waterspouts occur in an area enclosed by two lines. This leads to the statement "In the area bounded by these curves, conditions are favourable for the development of waterspouts. Outside this area, waterspouts are not likely to occur." Towards the top right of the nomogram I would think that conditions for waterspouts would be ideal, that is a large difference in sea and 850 mbar temps and very deep convective clouds. My feeling is that these conditions are extremely rare (or just never exist) which is why waterspouts were not observed under those conditions.

This method does seem to work well and would be interesting to apply to waterspout events along the east coast of Australia.

[Jimmy Deguara]

I would suspect that waterspouts occur in conditions with a recognised boundary similar to what occurs in landspout scenarios.

Generally, steep lapse rates until cloud base is another key indicator. In the case of landspouts, extreme heat at the surface achieves this. In the case of waterpouts, relatively warm ocean temperatures or extremely cold air aloft are often observed when waterspouts are observed. In all cases of videos that I have observed, a distinct boundary can be observed that the waterspout traverses.

Regards,

Jimmy Deguara