Oct 19

Met Office: Storm Brian to arrive this weekend


An intense low-pressure system that is forecast to affect southern Britain on Saturday has been named as Storm Brian by Met Éireann.

The Met Office’s Irish partner took the decision earlier today to issue an Orange warning for some parts of Ireland on Saturday because of expected impacts across the Irish Republic. Under the collaboration between the Met Office and Met Éireann a storm will be named when it has the potential to cause an amber/orange or red warning.

Image: Met Éireann

Today the Met Office updated their Yellow wind warning for strong southwesterly winds on Saturday from 4am covering parts of southern and western England and South and West Wales. Currently the Met Office has no plans to issue an Amber wind warning for any part of the UK, but the situation will be under continual review.

Chief Forecaster Dan Suri said: “Storm Brian is expected to bring strong winds to southern and western areas early on Saturday morning. The first and most significant land-based impacts will be in the southwest of Ireland, hence the Amber warning from Met Éireann. At the moment, we don’t expect the same level of impacts for the UK.

“As we go through Saturday morning and early afternoon the strong southwesterly winds affecting the South West will transfer east and slowly change direction as they will become westerly towards the end of the warning period.

“Gusts exceeding 50 mph are expected widely within the warning area, with gusts of around 70 mph along exposed coastal areas. These are expected to coincide with high tides, leading to locally dangerous conditions in coastal parts.”

Before it makes landfall, the system is undergoing explosive cyclogenesis far out in the Atlantic. However, by the time it reaches Britain and Ireland this phase is expected to be complete and it will be a mature, deep low, bringing strong winds with the potential to affect travel over the weekend. The Met Office and Met Éireann will continue to review the situation ahead of the system’s arrival.

As the system is expected to bring strong gusts during Saturday, there is the obvious potential of risk to travellers. RAC spokesman Pete Williams said: “Drivers encountering high winds are advised to reduce their speed, ensure they hold the steering wheel firmly and be prepared for sudden gusts, debris and even fallen branches in the road.  Allow plenty of room between your vehicle and the next and take extra care when overtaking cyclists, motorcyclists and lorries as they are susceptible to being blown around easily by side winds.  Be extra cautious when driving on exposed roads, high ground and across bridges where again sudden gusts can blow you off course.

“When you reach your destination consider parking safely avoiding trees, overhanging telephone wires and things which could represent a falling danger.”

The strongest winds in coastal areas, gusting up to 70mph, are expected to coincide with high tides, leading to potentially dangerous conditions for local coastal communities.

Alison Baptiste, National flood duty manager for the Environment Agency, said: “Strong winds are expected across southern England on Friday night and into Saturday. Some coastal floodingis possible along the south and south-west coasts of England, especially around the times of high tide, with large waves, spray and some overtopping of coastal defences.

“We urge people to stay safe along the coast and warn against putting yourself in unnecessary danger by taking ‘storm selfies’ or driving through flood water – just 30cm is enough to move your car. Environment Agency teams are on the ground checking defences and taking precautionary measures such as closing tidal gates.

“We’re working with partners including the Met Office and local authorities to monitor the situation and are ready to respond as necessary.Where necessary we will issue flood warnings and alerts. You can check whether you’re affected at www.gov.uk/flood.”

Under the guidelines of the storm naming collaboration, an Amber wind warning triggers the naming process. Storm Brian will be the second named storm of the season, following Aileen which affected parts of the UK on 12–13 September 2017.

The system is typical for the time of year and it has developed mainly as a result of a contrast in temperatures either side of the jet stream, with cooler temperatures to the north and warm temperatures to the south. Ex-Ophelia which affected Ireland and Britain on Monday and Tuesday had a different origin as it developed from a hurricane in the tropical Atlantic. Therefore, Ophelia’s original name was continued rather than using the next predetermined name from the UK and Ireland’s storm-naming process.

Oct 10

THE SOUTH AFRICAN WEATHER SERVICE: Severe thunderstorms wreak havoc in Gauteng on 9 October 2017; further warnings for KwaZulu Natal and Eastern Cape on 10 October 2017

10 October 2017 Severe thunderstorms with heavy downpours, strong damaging winds and large hail, hit parts of Gauteng and surrounding provinces on the afternoon of the 9th October 2017. Areas that were most affected were the West Rand District, City of Johannesburg and Ekurhuleni Metropolitan Municipalities. There were also 2 sightings of tornadoes in Ruimsig (adjacent to Roodepoort and Krugersdorp) and Eloff, near Delmas (Mpumalanga). Other provinces affected were the eastern parts of North, West, eastern Free State, KwaZulu-Natal, Mpumalanga and Limpopo. Extremely large hail (golf ball to tennis ball size) was also reported near Krugersdorp. Elsewhere in the Free State, a tornado was also observed near Bethulie yesterday.

Extensive damage to property was reported, which included the Cradlestone Shopping Mall in Roodepoort, where a roof partially collapsed, as well as numerous formal and informal dwellings which were completely destroyed. This resulted in more 100 people being displaced from their homes. Some roofs were ripped off residential dwellings and small office complexes in Krugersdorp and Roodepoort. Major roads were also affected by the flooding and resultant debris that were caused by the storm. At this stage, one death has been reported as well as a number of injuries.

Weather System
On the 9th October 2017, a line of thunderstorms developed east of a cut-off low pressure system which was situated over the western parts of the country. These storms developed through the central parts of the central parts of the North West and northern Free State, and then started moving eastwards. Due to prevailing favourable conditions (including abundant low-level moisture and strongly *sheared airflow in the lower portion of the storms), some of these storms developed into supercell thunderstorms. Supercell storms are the most intense class of thunderstorm and are characterised by a deep rotating updraft, are generally very long-lived (a lifespan of a few hours) and are associated with some sort of severe weather (one or more of large hail, tornadoes, strong winds and urban flooding) in at least 90% of cases. (*wind shear occurs when there is a marked change in wind speed and/or wind direction, across a short vertical distance)

Guidance issued by SAWS
The South African Weather Service issued a watch on Sunday afternoon (for Monday) for severe thunderstorms in places over the eastern parts of North West, eastern parts of the Free State, northern and central parts of KwaZulu-Natal and in places in Gauteng, Limpopo and Mpumalanga. This was upgraded to a warning on Monday afternoon as thunderstorms moved into the province from the west. These warnings were also carried extensively on social media channels of Twitter and Facebook.
A severe thunderstorm warning is issued by the South African Weather Service when a thunderstorm is expected to be associated with one or more of the following severe weather criteria*;
• Hail of greater than 19mm diameter. Alternatively, large amounts of small hail
• A tornado
• Wind gusts of 50 knots (93 km/h) or more
• Heavy downpours leading to localised urban or flash flooding

*This is closely aligned with international practise, particularly with respect to USA as well as Australia
Upcoming expected severe weather
The weather system that caused this weather has now moved to the east and most of the areas affected by yesterday’s storms can now expect predominantly sunny weather. There is however still a warning for heavy rain over KwaZulu-Natal (we have already received report of heavy rain and flooding in and around Durban) and eastern parts of the Eastern Cape before the weather system moves off the country later today (Tuesday). Thunderstorms are expected to return to the country on Saturday.
The South African Weather Service will continue to monitor further developments during this period and will issue subsequent updates as required. Furthermore, the general public are urged to regularly follow weather forecasts on television and radio. Updated information may also be accessed on www.weathersa.co.za as well as via the South African Weather Service Twitter account @SAWeatherServic