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| Remnants of Gonzalo – Analysis and Outlook By Matt Hugo - October 18, 2014 | |
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| Tweet Topic Started: 18 Oct 2014, 03:42 PM (56 Views) | |
| Audi-Tek | 18 Oct 2014, 03:42 PM Post #1 |
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Remnants of Gonzalo – Analysis and Outlook By Matt Hugo - October 18, 2014 By Matt Hugo - 13:05 ![]() OVERVIEW: Confidence is now increasing, given latest model guidance, that the remnants of hurricane Gonzalo will under-go development into quite a potent area of low pressure as it crosses the UK late in the day on Monday and overnight into Tuesday. There remain some uncertainties over the details, especially regarding just how strong winds will become, but what can be said is that a temporary spell of very wet and windy weather is now likely during the overnight period of Monday and into Tuesday. ANALYSIS: Firstly we will take a current look at where Gonzalo is and the system remains a fully-fledged hurricane given its structure and where it is located after passing over Bermuda yesterday. The system is being driven northwards towards the far east of Newfoundland as an upper trough, over the eastern side of the USA, approaches the hurricane. This will essentially ‘lift’ the system out of the tropical Atlantic and up into the North Atlantic where it will under-go extra-tropical transition (the transition of going from an actual hurricane, to a north Atlantic depression). The red arrow highlights the current expected track in the next few days… ![]() The particularly important aspect of the forecast is what happens when the system approaches the UK during the course of Monday and then as it crosses the country overnight into Tuesday. Think of the jet stream like a vacuum cleaner, it allows air to rise rapidly, especially under certain conditions. Rising air creates clouds and precipitation, but importantly the jet stream is what helps to deepen areas of low pressure which need ‘lift’ and energy to develop. Sometimes the jet stream doesn’t interact with a surface low pressure properly and as a result surface low pressure systems don’t really develop. However, on another occasion the jet stream interacts with a surface low pressure system in the right way to allow the low pressure to deepen and thus allowing the low pressure to bring strong winds and heavy rain. It is sort of like a surfer trying to catch a wave; If the surfer misses the wave (the energy) then he is left behind and not much happens. However, if the surfer ‘catches’ the wave then he is propelled forward due to energy and it is the same principle with regards to the jet stream interacting with a surface low pressure properly that will allow it to develop. At the moment there is model-wide agreement now that the jet stream will interact with the remnants of hurricane Gonzalo as it crosses the North Atlantic and moves across the UK overnight on Monday. This is highlighted on the below images. I’ve circled the approximate location of the remnants of Gonzalo at 1800GMT on Monday evening. The deep red colours on the image on the right highlighting plenty of energy associated with the system. Importantly though is the image on the left. Note how the jet stream (the dark blue colours) is approaching the low pressure just to the rear of it. This is a crucial aspect of the interaction of the jet stream on a surface low pressure to allow it to deepen and that is exactly what is now expected. ![]() The 10KM HRES model for late Monday night and then into Tuesday morning highlights well what is forecast to happen and is for a zone of heavy and perhaps squally rain and showers to quickly sweep across many areas of the UK on Monday night with gales immediately ahead of this rain band. As the low pressure begins to clear then this is when the strongest winds may well occur with gales or severe gales (gusts up to 60mph) just to the rear of the low pressure across Scotland and N England in particular at the moment. ![]() The system is expected to come and go very quickly and by the middle of Tuesday will be well to the east of the UK, so it is a ‘short and sharp’ spell of inclement conditions. However, given that the timing of the strongest winds and some of the heaviest rain may well be into the early hours of Tuesday and perhaps during the rush hour period of Tuesday morning then caution is advised and some travel disruption could well occur on Tuesday along with possible felled trees, seeing that some trees remain in leaf. One other interesting aspect is that as the system clears it will introduce a much cooler, if not colder air mass from the north-west. As a result precipitation is likely to turn to sleet and snow above 2000ft or so across Scotland with some significant snowfalls across the hills and mountains and the 10KM model is picking up on that, as highlighted by the snowflakes on the image on the right. We’ll keep you updated and more information on this will be within the Weekly Analysis tomorrow and we will then follow this up with a more detailed final analysis on Monday to keep you all up to date, but be prepared at least for a potential stormy spell of weather late Monday and into Tuesday. Chief Forecaster: MH Source .................... http://www.ukweatherforecast.co.uk/remnants-gonzalo-analysis-outlook/#sthash.X3bUyKy4.dpuf |
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8:08 PM Jul 11