Tropical storm DANNY westbound

General overview Wednesday 19th August 2015

The subtropical swirl we described yesterday is now shuffling around indecisively, centred some 350 miles of Cape Hatteras and strengthening gradually and may reach subtropical storm status over the next few days. It is likely that this will move slowly to the southeast for a couple of days before turning to the north when it will track towards New England and the Canadian Maritimes over the weekend and early into next week. The chances of this having impact ashore are fairly remote but a sweep close to Nova Scotia or Newfoundland is not out of the question

Today's headline news is tropical storm DANNY. Most addressees will be receiving regular updates on this – I received 135 emails in five hours overnight, most of them being highly technical speculation with limited value – so we will continue to stick with our daily update for those who only need a simple overview, but may increase frequency if there are significant developments or landfall is imminent. The latest update we have is that DANNY is centred 1200 miles east of Barbados and westbound at 10 knots with winds of 45 gusting 60 knots and a windfield of just 45 miles. This has a current hurricane severity rating of 3 (1 size, 2 intensity) and a predicted maximum of 10 (3 size, 7 intensity), although I suggest this might be a little low and winds in excess of 85 knots may be on the cards as this approaches the Caribbean in about four days time as a category one hurricane. DANNY has crept north of track which introduces two development factors. Slipping north of the fertile wet air belt will cause the storm to brush the remains of the Saharan dry air belt which has dominated the region thus far this season. As the storm passes over the cobbles of dry air, vertical convection will suffer and may hinder development, albeit briefly. Secondly, this begins to take the storm away from the upper level shear barrier which has provided a solid protective wall for the Caribbean this season. Add this to a leisurely ground speed, we have a storm which will develop over the next few days, probably reaching hurricane strength before stabilising for a couple of dry days, then digging again as it arcs away towards the north. This lessens the risk to the Leeward Islands to the cost of the islands of the north east Caribbean and perhaps a long shot, Hispaniola or the Bahamas. Whilst the Gulf of Mexico is warm, wet and willing, the chances of this system making it that far west are slim – at present.

While all eyes are on DANNY, a convoy of low pressure cells is lining up to the south of the Sahara desert and likely to produce more viable disturbances of the coming week.

This will be a mucky couple of days for anyone at sea in the western tropical Atlantic, otherwise, stand easy. 

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