What is Bertha going to do?

Image: National Hurricane centre (NOAA)
Post-Tropical Cyclone Bertha Image courtesy: National Hurricane Centre (NOAA)

[Update – you can read the latest here]

You may have heard lots in the news about ex-hurricane Bertha, such as this story in Monday’s Daily Telegraph



or this just a few hours ago from Scotland Now



Both stories were amongst the first to come up on a google search but a fair example of some of the media coverage so far.

Bertha is not expected to reach the British Isles for another four days, Sunday and is only now coming into a reliable model forecasting range. Unfortunately, the current forecast for the British Isles is anything but reliable as often happens during Met Office have been reporting this storm system. Monday;

A Tropical Storm called Bertha, which is currently in situated off the east coast of the US, could head towards Europe over the next week – so what’s the outlook?

Forecast tracks for Bertha, which was a hurricane but has now been downgraded to a tropical storm, suggest it will head north – staying offshore from the eastern coast of the US before turning to track east across the Atlantic.

While all forecast models suggest the storm will head in the general direction of UK and continental Europe, there remains a lot of uncertainty about exactly what it will do.

One certainty is that as the storm heads north away from the very warm seas which drive its power, it will lose strength and become what’s known as an extra-tropical storm – so we won’t be seeing a ‘hurricane in Europe’, but there is a chance we could see a fairly active summer storm.


This was their take on Wednesday;

Image courtesy Met Office
Image courtesy Met Office

Tropical Storm Bertha is currently off the north east coast of the US and is likely to become an ‘extra tropical storm’ on Thursday.

It’s then expected to track across the Atlantic – and while there are still a number of possible outcomes, it looks increasingly likely that the UK will miss any serious impacts from ‘ex Bertha’.

The Met Office has been assessing the likelihood of the UK seeing any effects from Bertha by using our own forecast model alongside models from other world-leading forecast centres.

At the moment the majority of forecasts from those models suggest ex Bertha will track to the south of the UK as a relatively weak low pressure system.

In fact it’s debatable whether this is even ex Bertha, as the storm declines to such an extent as it comes across the Atlantic that it fragments.

Some of the warm air which it drags across then leads to a new weak low which generates an area of heavy rain. This could move across northern France and possibly clip eastern parts of the UK on Sunday.

A much smaller number of model outcomes suggest ex Bertha will move across the UK as a more distinct feature which could bring some strong winds and heavy rain. Because these outcomes are in a minority, however, they are less likely.


However, as of this evening the latest models – including the Met Office’s – look to have changed and show this system once again further North crossing the UK – although the options range from a rather disorganised system to a more organised one with blustery winds. They are all expected to bring rain as a trough remains in or around the UK  bringing unsettled weather.* The uncertainty looks to continue.

What does Piers have to say?

Bertha  is (eg Aug 6th) is following general path of WeatherAction storm rules and will head more to FRANCE than Br+Ir and be ~in line with WeatherAction Euro-maps. The double R5 hit at the same time will force hot from South into Britain – contributing to WeatherAction hot August (espec England Mids+S/E) forecast.

I spoke with Piers earlier today before the latest model updates and the above statement was as discussed (thanks for the main blog update Piers!). However even though Bertha is unlikely to be of much consequence as it does not fall in an active period it should be closely watched in the coming days. There is already a yellow Met Office warning in force for Friday for the South east of England. Localised flash floods and thundery downpours are always a risk at this time of year.

You can watch Friday’s system and whatever remains of Bertha on Sunday by using the Radar/Satellite/Lightning links at the top following page:


You can also follow also the comments offering the observations over at the main WeatherAction site.

Some Images

Earth facing coronal hole CH 630
Image National Oceanic and Atmospheric Administration (NOAA)
Latest Jet stream
Image courtesy San Francisco State University

These are the last three GFS 12z runs which show an increasingly southerly approach. I will add the next 12z update tomorrow. [Bertha is the ‘L’ to the left hand side of the images]





* this was the latest available forecast update issued at: 1700 on Wed 06 Aug 2014

Outlook for Friday to Sunday:

Often unsettled with sunshine and showers. More persistent rain is likely in the south and east on Friday. Chance of wet and windy weather Sunday, most likely in the south.

Issued at: 1700 on Wed 06 Aug 2014

UK Outlook for Monday 11 Aug 2014 to Wednesday 20 Aug 2014:

Any lingering wet and windy weather in the east should clear on Monday to leave a breezy spell with scattered showers. However, further rain is then likely to spread from the west to most parts except the far north. Conditions remain fairly unsettled for the rest of the week, with cloudy, wet spells interspersed with brighter but showery conditions. Breezy at times, especially in the north. Temperatures generally near or slightly below normal, and feeling cool in the stronger winds and heavy rain. Thereafter, a north/south split looks most likely to become established, with outbreaks of rain or showers and breezy conditions towards the north, the best of any drier and brighter weather in the south. Temperatures largely near or just below normal, perhaps warm at times in the southeast.


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