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- 1. Skysail Training © K M Bater 2010 1 of 20 © 2009 SKYSAILTRAINING 9th November 2009 Feedback is welcome Click on www.skysailtraining.co.uk for on line Colregs test and CEVNI test and to buy Weather, Colregs, VHF and more navigation skills charts Test Yourself - Online Exam RYA Day Skipper and Yachtmaster ICC / BSAC Seamanship Met - Weather Exam / Assessment Meteorology Weather at Sea Mouse click or Page Down to start
- 2. Skysail Training © K M Bater 2010 2 of 20 SKYSAIL SKILLS CHARTS http://www.btinternet.com/~keith.bater/navigation_skills_charts.htm Day Skipper Chartwork Weather VHF Extracts from Skysail Skills Charts on the essential navigation subjects – all summarised on A4 laminated charts. For full details click link above
- 3. Skysail Training © K M Bater 2010 3 of 20 Before the Meteorology tests • Here is the full weather presentation if you need it (2MB): www.btinternet.com/~keith.bater/weather_for_course.pdf
- 4. Skysail Training © K M Bater 2010 4 of 20 Forecasts Where would you find weather forecasts? On land At sea TV National radio Local radio Newspapers Teletext Web Barometer Mobile phone BBC radio Coastguard VHF Metfax to PC Navtex Barometer Observation Mobile phone Day Skipper Weather
- 5. Skysail Training © K M Bater 2010 5 of 20 Forecasts What is the sequence of the Shipping Forecast? Gale warnings Day Skipper Weather General Synopsis at time of issue Wind now - direction and force Wind later Sea state Weather - fair, rain, etc Visibility
- 6. Skysail Training © K M Bater 2010 6 of 20 Shipping Forecast Terms What do the following mean? Within 6 hours Imminent Soon Later 6 to 12 hours After 12 hours of the time of issue of the forecast Very poor Poor Moderate Good < 1000 metres visibility < 2 Miles > 5 Miles 2 - 5 Miles Fair No precipitation 1.25 – 2.5 2.5 – 4.0 4.0 – 6.0 Moderate Rough Very rough Wave height m Day Skipper Weather
- 7. Skysail Training © K M Bater 2010 7 of 20 Wave height What factors affect wave height? Wind speed and duration Tide speed and direction wind against tide gives higher waves Depth of water Fetch - the distance over which the wind blows Swell - the wave pattern before the current weather 1 2 3 4 5 Day Skipper Weather
- 8. Skysail Training © K M Bater 2010 8 of 20 Wind How do you define the following? Direction Cyclonic Veering Backing Direction from which wind blows Changing direction clockwise Rapid changes in wind direction (Possibly at the centre of a depression) Changing direction anticlockwise Day Skipper Weather
- 9. Skysail Training © K M Bater 2010 9 of 20 Pressure / Wind / Waves What is likely if the pressure has changed by 6 millibars in the last 3 hours? A gale (whether the change is rising or falling) Day Skipper Weather From these descriptions estimate what the Beaufort wind force is: a) Moderate waves, many white crests. b) Sea heaps up, spray, breaking waves, foam blows in streaks. Force 5 17-21 knots Force 7 28-33 knots
- 10. Skysail Training © K M Bater 2010 10 of 20 Fronts / Buys Ballot How do you define the following? Occluded Front Buys Ballot’s Law in the Northern Hemisphere, if you stand with your back to the wind, the area of low pressure is to your left and the high pressure to the right. An occluded front is formed when the faster moving cold front overtakes and merges with the warm front. Typical weather is cloudy, with light rain and poor visibility Warm Front Cool air Warm air Advancing cold air Cold Front Occluded Front Day Skipper Weather
- 11. Skysail Training © K M Bater 2010 11 of 20 Depressions What is the weather and wind at A, B, C, D, E? A B C L H D E Day Skipper Weather Fair Light winds Clear, bright Showers Good visibility Wind veers and increases Cumulonimbus Heavy rain Thunder Lightning Squalls Broken cloud Showers Very poor visibility Wind steady Light Rain Wind backs Heavy rain Poor visibility Wind increases
- 12. Skysail Training © K M Bater 2010 12 of 20 Clouds What type of clouds and what do they signify? Cumulus - fair weather Cumulonimbus - thundercloud, squally, lightning. Cold front. Cirrus - can indicate an approaching depression Yachtmaster Meteorology
- 13. Skysail Training © K M Bater 2010 13 of 20 Sea Breezes Sea breezes are caused by unequal heating of land and sea surfaces. During the day, especially in summer, solar radiation heats the land surface to become warmer than the sea surface which stays cold all summer. The temperature difference rises to a maximum around mid afternoon. The warm air rises over the land and cool air from the sea is drawn in, setting up an onshore wind. As the heating effect increases, the sea breeze strengthens, and may reach 15 knots (F4). A land breeze develops at night as the land cools relative to the sea and an opposite but weaker circulation sets up. What is a sea breeze? What causes it? Yachtmaster Meteorology
- 14. Skysail Training © K M Bater 2010 14 of 20 Sea Fog 1.What causes sea fog? 2.In which season is it most frequent? 3.Will there be wind? 4.What makes it clear? It occurs when warm air flows over a cold sea surface (advection flow). Spring / early summer when the sea is still cold. Yes A change in wind direction or sea temperature Yachtmaster Meteorology
- 15. Skysail Training © K M Bater 2010 15 of 20 Land Fog 1.What causes land fog? 2.In which season is it most frequent? 3.Will there be wind? 4.What makes it clear? It occurs when land cools overnight by radiation of heat. The air cools and moisture condenses to form fog. Late Autumn / Winter when pressure is high and there is no cloud. No. Land fog can form in valleys and drift out to sea. The heat of the sun the following morning. Yachtmaster Meteorology
- 16. Skysail Training © K M Bater 2010 16 of 20 Coastal Winds With the gradient wind as shown, what will the wind be on the coast lines? Winds diverge. Coastal wind is weaker Winds converge. Coastal wind is stronger Yachtmaster Meteorology
- 17. Skysail Training © K M Bater 2010 17 of 20 Depression Cold Front Cold Air Warm Sector Cool Air 20,000 ft East West Nimbostratus Cirrostratus Altostratus Cumulus Cumulus Cumulonimbus Cirrocumulus Altocumulus Stratocumulus 600 M 300 M 200 M PASSAGE OF A DEPRESSION Cirrus Warm Air Fractostratus WIND Strong gusts Veering sharply Squalls Steady Veering Backing & increasing WIND PRESSURE Rising, then steady Rising quickly Steady Steady Falling PRESSURE RAIN Sunny, squally showers Heavy rain, thunder, hail Light rain Drizzle Becoming heavier and prolonged RAIN VISIBILITY Good except in showers Poor in rain Poor Fog Poor Deteriorating VISIBILITY TEMP Cold Falls Warm Warm Rising TEMP
- 18. Skysail Training © K M Bater 2010 18 of 20 Cold front Warm front Warm sector F Depressions What is the weather at A, B, C, D, E, F ? Nimbostratus Heavy rain Poor visibility Wind increases Cumulonimbus Heavy rain Lightning Thunder Squalls A E D B C Cirrus, fair Cirrostratus Altostratus Light Rain Wind backs Pressure falls Clear, bright Cumulus Showers Good visibility except in showers Wind veers sharply and increases Pressure rises Broken cloud Alto cumulus Showers Very poor visibility Wind veers, steady Pressure is steady Yachtmaster Meteorology
- 19. Skysail Training © K M Bater 2010 19 of 20 Pressure Systems What is the likely wind at A, B, C ? Variable, light SW, light NW, strong SSE, strong C L L A H L B H D L Deep depression Yachtmaster Meteorology
- 20. Skysail Training © K M Bater 2010 20 of 20 Cold front Warm front Warm sector END Yachtmaster Meteorology