It’s always amazing to see the hype and misleading information spouted by the tabloids at this time of year when there’s mention of a former tropical cyclone coming our way.

This is classic of the Daily Express.

To support a hurricane, you MUST have water temperatures of 26C or greater with little to no mid and upper level wind shear. TROPICAL cyclones, AKA Tropical Storms or hurricanes are just that, TROPICAL and develop completely different inner characteristics including a warm core. There are no fronts nor are they driven by warm/cold air masses surrounding them like mid-latitude, baroclinic systems.

The problem we have is that the media, such as the express, like to twist reality, hype things to the max in order to sell their newspapers. This causes confusion, a great deal of misinformation and has forecasters explaining practically every late summer/early autumn period, why we’re NOT getting a hurricane but ‘former’ system that at one time in it’s past, was a tropical entity.

Bertha, like hundred of other former tropical systems, we’re born in a tropical, warm, moist environment and developed as a tropical cyclone but once it gets further north and leaves the low latitudes and reaches the mid-latitudes, waters become too cool and upper level winds increase. Ever wondered why it can take up to 10 days for a tropical system to cross the Atlantic from Africa to the Caribbean (light easterly trade winds) while they can reach the UK from near Bermuda within 36 to 48 hours. That’s because they catch the influence of the westerlies AKA the jet stream. Lows in more northerly latitudes are much more spread out, sometimes spanning well over 1,000 miles with a very different type of wind field and structure.

Tropical cyclones have a much smaller, more symmetric and tighter wind field.

The trouble is, these lows (once tropical) can still pack a punch as a regular, north Atlantic low. Some of these systems have been known to cause damage and disruption and Bertha, like Katia of 2011 could still pack a punch bringing flooding rain and gales, even severe gales. Many think that these systems come up here and are weaker affairs. How many times have you heard folks say, We’re meant to get the ‘tail end’ of a hurricane. There’s no tail end, there’s no hurricane, we can get glancing blows or a direct hit from a low that’s simply a feature of our weather year round. Some pass with little more than cloud and a sprinkle, others do make their presence felt.

Note in the below map, the sharp cooling of water away from the tropical region. Our water up here is nearly 20C cooler than in the region where waters must be a certain threshold to support tropical development, ie 26C+.

Current sea surface temperatures.

Bertha’s remnant low is still projected to make a UK impact this weekend.

Bertha undergoes two strengthening phases, one as a depression, storm and hurricane in the tropics while it crosses the ITZC zone from Africa towards the Caribbean, then once it recurves, deflected by a trough over the United States, crosses back over the Atlantic on the north side of the same semi-permanent high pressure system (Mid-Atlantic ridge) as a barclinic low and intensifies along the jet stream where warm and cold air masses meet. Central pressure is likely to lower as a storm near the UK than it was as a hurricane. Whether it can generate 80 mph winds like it did remains to be seen.

Think it can’t? Katia brought down trees back in Sept 2011 over Scotland with winds clocking 80 mph.

As per current model runs, it’s looking more like rain rather than wind will be the greatest threat from this system.

Great graphic via Reigate Grammar School Weather Station shows just how frequently former tropical cyclones pass by our part of the world.

Did you know that the Great Storm of October 1987 was in fact former Hurricane Floyd which hit the US Carolina coast. Strongest winds at the coast where just 75 mph with pressure above 990mb but with different properties driving the very same system, it hit Western Europe with winds in excess of 140 mph and pressure fell to 953mb.

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Tags: bertha, hurricane bertha, hurricanes, tropical cyclone